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Interactions & Safety

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Laboratory data show that curcumin can affect liver enzymes and platelets [1][2]. A review advises caution [3]; in a short observation in patients, INR and bleeding time did not change under a curcumin product [4]. Talking to a doctor or pharmacist is sensible.

In short

Lab: curcumin inhibits CYP3A4 and CYP2C9 (recombinant enzymes) and platelet aggregation (isolated platelets)
Review: interactions with anticoagulants possible, clinical data scarce
Short patient observation (10 days): INR and bleeding time unchanged
Studies concern supplements, not kitchen amounts of the spice
Discuss with a doctor or pharmacist

What's behind it

Two mechanisms are under discussion. First, in laboratory tests with recombinant enzymes, curcumin inhibited the liver enzymes CYP3A4 and CYP2C9 (IC50 about 12 and 15 µM); both are among the principal drug-metabolizing enzymes [1]. Second, in isolated platelets it inhibited aggregation triggered by platelet-activating factor or arachidonic acid (IC50 about 20–25 µM) and the formation of thromboxane A2 (IC50 70 µM) [2]. These are cell and enzyme experiments; they do not show whether this matters in the body at usual intakes.

What the sources show

A review (Bahramsoltani et al., 2017) describes that curcumin given together with drugs such as cardiovascular drugs, antidepressants, anticoagulants, antibiotics, chemotherapeutic agents and antihistamines can change Cmax and AUC, probably through inhibition of CYP enzymes and P-glycoprotein. It found only one clinical trial with a significant change; in vitro and animal data were not enough to judge clinical interactions reliably. The authors advise physicians to remain cautious [3].

In a clinical observation (Hu et al., 2018), patients taking acetylsalicylic acid, ticlopidine or clopidogrel (for at least two years) received a curcumin-phospholipid product (Meriva®) for 10 days; bleeding time afterwards was not significantly different. In patients on warfarin or dabigatran, the INR after 10 days was not significantly different from baseline [4]. This applies to one specific product and a short period.

A review of supplements (Dobre et al., 2025) lists curcumin alongside ginkgo, ginger and ginseng as a substance that may increase bleeding risk in combination with antithrombotic therapy [5]. The EMA monograph on turmeric rhizome (traditional use for digestive complaints) states "None reported" under interactions [6].

On tolerability: in healthy volunteers, single doses of 500 to 12,000 mg of a curcuminoid extract caused only minimal toxicity that was not dose-related; no curcumin was detected in serum up to 8,000 mg. The participants took no medication [7].

What this means in practice

Anyone taking warfarin, a direct oral anticoagulant, acetylsalicylic acid or similar agents is well advised to discuss curcumin products with a doctor or pharmacist beforehand; especially for extracts, the effect on clotting values has not been settled. There are no studies on turmeric as a kitchen spice combined with blood thinners.

Limits of the statement

The enzyme and platelet data come from laboratory experiments; the clinical observation concerns a single product over 10 days. The sources contain no long-term data on bleeding events. This answer does not replace medical advice.

Common follow-up questions

Possibly. In laboratory experiments curcumin inhibited platelet aggregation and thromboxane A2 formation (Shah et al., 1999) PMID 10484074; these were cell experiments, not a human study. Turmeric may also increase the risk of bleeding with warfarin or antiplatelet drugs (LactMed, 2025) PMID 30000906. A review also lists anticoagulants among the drugs whose levels curcumin can alter (Bahramsoltani et al., 2017) DOI. If you take blood-thinning medication, talk to your doctor first.

This cannot be stated in general. In laboratory experiments, curcumin inhibited platelet aggregation (Shah et al., 1999) PMID 10484074. Turmeric may increase the risk of bleeding when taken together with warfarin or antiplatelet drugs (LactMed, 2025) PMID 30000906. If you take blood-thinning medication, talk to your doctor or pharmacist before regular use.

This should only be done after consulting a doctor and with monitoring. Turmeric may increase the risk of bleeding with warfarin (LactMed, 2025) PMID 30000906. A review lists anticoagulants among the drugs whose levels curcumin can alter and advises physicians to be cautious (Bahramsoltani et al., 2017) DOI.

A review describes that curcumin can alter the levels of co-administered drugs, such as cardiovascular drugs, antidepressants, antibiotics, chemotherapeutics and antihistamines, probably through inhibition of CYP enzymes and P-glycoprotein; clinical data are scarce, however (Bahramsoltani et al., 2017) DOI. In laboratory experiments, a curcuminoid extract inhibited CYP2C9 and CYP3A, among others (Volak et al., 2008) DOI. If you take medication, talk to your doctor or pharmacist first.

Talk to your doctor before taking turmeric extracts if you take medication, have gastrointestinal complaints or plan longer use. Reasons: drug interactions are possible, although the clinical evidence is thin and physicians should remain cautious (Bahramsoltani et al., 2017) DOI. In addition, nausea, diarrhea and allergic reactions have been reported, and bleeding risk may increase with warfarin (LactMed, 2025) PMID 30000906.

Side effects: Learn more about the safety profile and possible interactions in detail.
Effects of turmeric: An overview of areas of use and general properties of curcumin.
Intake & bioavailability: Everything on optimal absorption and how the body best utilizes curcumin.

References

[1] Shamsi, S. et al. (2017). Curcumin, Piperine, and Capsaicin: A Comparative Study of Spice-Mediated Inhibition of Human Cytochrome P450 Isozyme Activities. Drug Metabolism and Disposition, 45(1):49–55. DOI: 10.1124/dmd.116.073213
[2] Shah, B. H. et al. (1999). Inhibitory effect of curcumin, a food spice from turmeric, on platelet-activating factor- and arachidonic acid-mediated platelet aggregation through inhibition of thromboxane formation and Ca2+ signaling. Biochemical Pharmacology, 58(7):1167–1172. DOI: 10.1016/s0006-2952(99)00206-3
[3] Bahramsoltani, R., Rahimi, R. & Farzaei, M. H. (2017). Pharmacokinetic interactions of curcuminoids with conventional drugs: A review. Journal of Ethnopharmacology, 209:1–12. DOI: 10.1016/j.jep.2017.07.022
[4] Hu, S. et al. (2018). Interaction study between antiplatelet agents, anticoagulants, thyroid replacement therapy and a bioavailable formulation of curcumin (Meriva®). European Review for Medical and Pharmacological Sciences, 22(15):5042–5046. DOI: 10.26355/eurrev_201808_15647
[5] Dobre, M.-Z. et al. (2025). Navigating the Effects of Anti-Atherosclerotic Supplements and Acknowledging Associated Bleeding Risks. International Journal of Molecular Sciences, 26(20):10183. DOI: 10.3390/ijms262010183
[6] European Medicines Agency, HMPC (2018). European Union herbal monograph on Curcuma longa L., rhizoma (EMA/HMPC/329755/2017), adopted 25 September 2018. ema.europa.eu
[7] Lao, C. D. et al. (2006). Dose escalation of a curcuminoid formulation. BMC Complementary and Alternative Medicine, 6:10. DOI: 10.1186/1472-6882-6-10

Reviews describe that curcumin affects inflammation and tissue build-up [1]. Clinical studies, however, used specially made preparations [2]; there are no studies on kitchen powder on open wounds. For wounds, medical advice is sensible.

In short

Studies use special dressings, gels or solutions, not kitchen powder
Foot-ulcer pilot (n = 15): curcumin latex dressing plus red light, ulcer 89.8 % smaller after 45 days
Scoping review: 19 clinical trials, inconsistent results
Market powders may be adulterated (dyes, lead)
Open, deep or infected wounds: have them assessed by a doctor

What's behind it

Reviews describe that in wound models curcumin reduces inflammation and reactive oxygen species and increases collagen deposition, granulation tissue and wound contraction. Its use is limited by low solubility, rapid metabolism and a short half-life; nanocarriers such as liposomes or nanoemulsions are therefore being developed [1].

What the sources show

A scoping review (Parvizi et al., 2025) evaluated 19 clinical trials, 14 of them randomised. Curcumin in various forms, topical and oral, improved wound healing compared with placebo or standard care in 89 % of the studies; no adverse events were reported in 84 %. The authors stress the large heterogeneity, which prevents consistent guidelines [2].

A pilot study (Gomes et al., 2025) allocated 15 people with diabetic foot ulcers to three groups of 5. The group with a natural-latex dressing containing curcumin liposomes plus red LED light reached a mean ulcer contraction of 89.8 % after 45 days, the standard-care control group 32.8 %, and the dressing-plus-light group without curcumin 9.7 %. The sample is very small, and the combination with light therapy leaves the contribution of curcumin open [3].

In a multicentre randomised trial (Sanpinit et al., 2024), after 12 weeks 19 of 25 people with diabetic ulcers using a traditional Thai herbal solution (Ya-Samarn-Phlae) in addition to standard care achieved complete healing, versus 4 of 25 in the control group (76 % vs. 16 %). The preparation contains arecoline and α-mangostin besides curcumin, so the effect cannot be attributed to curcumin. In cell experiments of the same paper, Curcuma longa extract promoted the migration of human dermal fibroblasts [4].

On kitchen powder: a survey of Indian markets found the non-permitted dye metanil yellow in 17 % of loose turmeric powders [5]; in a study from eastern India, 30 % of 503 samples exceeded the lead limit, due to lead chromate adulteration [6]. There are no studies of kitchen powder on open wounds.

What this means in practice

The products studied are specially manufactured dressings or solutions. Spice powder from the kitchen is not comparable. For large, deep, poorly healing or infected wounds, especially with diabetes, seek medical help.

Limits of the statement

The clinical data are heterogeneous, partly very small (n = 15) and concern special formulations, in part combined with other active ingredients or light therapy. This answer does not replace medical or surgical wound care.

Common follow-up questions

In a scoping review of 19 clinical trials, curcumin improved wound healing compared with placebo or conventional care in 89% of the studies, but the trials were highly heterogeneous (Parvizi et al., 2025) DOI. In a pilot study of 15 people with diabetic foot ulcers, the group with a curcumin-containing latex dressing plus LED light (n = 5) reached a wound contraction of 89.8% after 45 days, the control group 32.8% (Santana et al., 2025) DOI.

We advise against it. Spice powder is not a sterile medical product; studies used defined formulations such as dressings (Parvizi et al., 2025) DOI (Santana et al., 2025) DOI. In addition, in a survey of 503 turmeric samples from eastern India, 30% exceeded the lead limit which is linked to adulteration with lead chromate (Forsyth et al., 2026) DOI. For open wounds, seek medical advice.

This is not established. In a small pilot study (15 people, 5 per group), diabetic foot ulcers treated with a curcumin-containing dressing plus LED light had contracted by 89.8% after 45 days versus 32.8% in the control group (Santana et al., 2025) DOI. In a trial of a multi-herb preparation that contains Curcuma longa among other ingredients, 76% of wounds were completely healed after 12 weeks versus 16% in the control group (Sanpinit et al., 2024) DOI; the effect cannot be attributed to curcumin alone.

We found no specific data on swallowed curcumin for wounds; the scoping review on wound healing covers oral and topical forms without separating the result (Parvizi et al., 2025) DOI. For oral lichen planus (a chronic inflammatory mucosal disease, not a wound), a trial with 2,000 mg of curcuminoids daily for 7 weeks was stopped early for futility after the interim analysis showed no significant difference from placebo (Chainani-Wu et al., 2007) DOI.

The duration cannot be stated in general: the trials reviewed used curcumin in very different doses, forms and treatment durations (Parvizi et al., 2025) DOI. In the pilot study on diabetic foot ulcers, patients were followed for 45 days; by then the ulcer had contracted by 89.8% with the curcumin dressing plus LED light (control 32.8%) (Santana et al., 2025) DOI.

Read further

Want to go deeper into the subject? Here's where to continue:

Side effects: Safety profile, bleeding risks and side effects at a glance.
Benefits of turmeric: An overview of fields of application and therapeutic goals.
Intake guide: Worth knowing about absorption, bioavailability and the various formulations.

References

[1] Kumari, A. et al. (2022). Wound-Healing Effects of Curcumin and Its Nanoformulations: A Comprehensive Review. Pharmaceutics, 14(11):2288. DOI: 10.3390/pharmaceutics14112288
[2] Parvizi, M. M. et al. (2025). A Scoping Review of Clinical Trials on the Efficacy of Curcumin and Its Formulations for Wound Healing. Journal of Cosmetic Dermatology, 24(12):e70615. DOI: 10.1111/jocd.70615
[3] Gomes, T. F. S. et al. (2025). A Natural Latex-Based Smart Dressing for Curcumin Delivery Combined with LED Phototherapy in Diabetic Foot Ulcers: A Pilot Clinical Study. Pharmaceutics, 17(6):772. DOI: 10.3390/pharmaceutics17060772
[4] Sanpinit, S. et al. (2024). Effectiveness of Ya-Samarn-Phlae in diabetic wound healing: Evidence from in vitro studies and a multicenter randomized controlled clinical trial. Journal of Ethnopharmacology, 326:117929. DOI: 10.1016/j.jep.2024.117929
[5] Dixit, S. et al. (2009). Surveillance of the quality of turmeric powders from city markets of India on the basis of curcumin content and the presence of extraneous colours. Food Additives & Contaminants: Part A, 26(9):1227–1231. DOI: 10.1080/02652030903016586
[6] Forsyth, J. E. et al. (2026). Systemic drivers of toxic food adulteration: lead chromate in turmeric across eastern India. npj Science of Food, 10(1):220. DOI: 10.1038/s41538-026-00867-8

The EMA lists no fertility data [1]. In laboratory tests, curcumin reduced sperm motility [2][3], and animal models showed protective effects on the testes [4][5]. Transfer to humans is not established.

In short

Human studies on fertility: none in the sources checked; EMA: no data
Lab: curcumin reduced motility of human sperm
Mouse models: partly protective effects on testes and sperm
Pregnancy and breastfeeding: not recommended per the EMA
When trying to conceive, discuss supplements with a doctor

What's behind it

The question has two sides: does curcumin act on sperm and reproductive organs, and what data exist for humans? The EMA monograph on turmeric rhizome states "No fertility data available" under fertility and advises against use in pregnancy and lactation for lack of data [1]. The other sources checked also contained no human study on turmeric or curcumin and fertility.

What the sources show

Laboratory tests with sperm: Human sperm lost motility in vitro in a dose- and time-dependent way. At 30 µg/mL it fell by 20 % after 30 minutes; at 300 µg/mL it was lost completely within 60 minutes; mitochondrial membrane potential decreased at all doses [2]. Another paper found a concentration-dependent decrease in motility, capacitation and acrosome reaction in human and mouse sperm. In mice, curcumin, especially given intravaginally, reduced fertility; the effect was reversible [3]. Both groups discuss this as an approach to a vaginal contraceptive, not as a consequence of ordinary diet.

Animal models with injury: In mice with cryptorchidism (undescended testes), curcumin (25–300 mg/kg for five weeks) improved sperm production and testicular tissue; the best effect was at 100 mg/kg [4]. A systematic review of 31 cell and animal studies describes protective effects of curcumin against chemically induced damage to the male reproductive system, mostly at 50–200 mg/kg; the authors call for further studies on dosing, bioavailability and long-term safety [5].

Uptake in the body: In healthy volunteers, no curcumin was detected in serum after single doses of 500 to 8,000 mg [6]. The sources do not show which tissue concentrations are reached at usual intakes.

What this means in practice

The sources allow neither a fertility-enhancing nor a fertility-reducing effect of turmeric at usual amounts to be inferred. Anyone who is pregnant or planning a pregnancy is well advised to discuss turmeric supplements with a doctor [1].

Limits of the statement

The data come from cell experiments and mice using isolated curcumin at concentrations and doses that cannot simply be transferred to usual intakes. Interactions with fertility medication were not examined in the sources. This answer does not replace medical advice.

Common follow-up questions

In a randomised trial in 60 men with fertility problems, sperm count, concentration and motility after 10 weeks of 80 mg curcumin nanomicelles daily were higher than with placebo (Alizadeh et al., 2018) DOI. In mice with cryptorchidism, curcumin improved sperm production (Wang et al., 2025) DOI. Both are single studies with special formulations; further research is needed.

This is not sufficiently established. According to the EU monograph, safety during pregnancy and lactation has not been established and use is not recommended due to lack of data EMA/HMPC/329755/2017. A review describes the data on curcumin in pregnancy as limited and mostly from animal and cell studies (Filardi et al., 2020) DOI; another review considers turmeric safe in pregnancy in animal studies but calls for human studies (Soleimani et al., 2018) DOI. Talk to your doctor.

In the laboratory, curcuminoids inhibited the activity of steroid-producing enzymes (CYP17A1, CYP19A1, more weakly CYP21A2), especially at higher concentrations (Rodríguez Castaño et al., 2019) DOI. In humans, findings are mixed: in women with PCOS, testosterone and SHBG after 1,000 mg curcumin daily for 12 weeks did not differ from placebo (Ghanbarzadeh Gashti et al., 2023) DOI, while in combination with metformin testosterone fell more than with metformin alone (Sohrevardi et al., 2021) DOI.

What's behind it

Curcumin is barely absorbed because it is rapidly metabolised in the liver and intestinal wall. In a study with healthy volunteers, serum levels were undetectable or very low after 2 g of curcumin alone [1].

What the sources show

Meals and fat: For eight commercial turmeric products, laboratory dissolution was lowest under fasted conditions and improved slightly in a gastric medium simulating a meal; the authors attribute this to the lipid content. No product released more than 40 % [2]. A review notes that fats, proteins and fibre can improve the stability and bioavailability of spice compounds, especially dairy for curcuminoids; most human studies examined only acute effects [3].

Piperine: In the same study in which 2 g of curcumin alone was barely detectable, co-administration of 20 mg piperine increased bioavailability by 2,000 % (154 % in rats) without side effects [1]. This is a small single-dose study. In laboratory tests, piperine inhibited recombinant CYP3A4 (IC50 2.1 µM) more strongly than curcumin (11.9 µM) [4]. Anyone taking medication should therefore clarify piperine-containing products with a doctor.

Dose: In 24 healthy volunteers, single doses of 500 to 12,000 mg of a curcuminoid extract caused only minimal toxicity that was not dose-related [5]. In a phase I study, 15 cancer patients took 0.45 to 3.6 g curcumin daily for up to four months without dose-limiting toxicity [6]. In a placebo-controlled trial of 60 healthy adults, gastrointestinal tolerance of a highly bioavailable extract (1,000 mg daily for 5 weeks) did not differ from placebo [7]. No maximum dose or dose-benefit relationship can be derived from these studies.

Liver: A review by the US Pharmacopeia describes rare cases of liver injury with turmeric or curcuminoid supplements, mostly after 1 to 4 months and generally resolving after discontinuation. With abdominal pain, dark urine or yellowing of skin or eyes, the USP advises stopping the product and seeking medical advice [8].

Groups needing caution: The EMA advises against turmeric in biliary and liver disease, gallstones, and during pregnancy and breastfeeding [9].

What this means in practice

According to these data, taking it with a meal containing some fat is a plausible approach; direct human studies on the amount of fat are lacking in the sources. Piperine-containing products and extracts are best discussed with a doctor or pharmacist if you take medication, have biliary or liver disease, or are pregnant or breastfeeding. See also interactions.

Limits of the statement

The absorption data come from laboratory tests and very small studies. The tolerability studies concern individual products and limited periods, partly in patients. This answer does not replace medical advice.

Common follow-up questions

No, not reliably. In a small study in healthy volunteers, the bioavailability of 2 g curcumin rose by 2000% with 20 mg piperine (Shoba et al., 1998) DOI. In a later randomized cross-over trial in 12 healthy adults, curcumin with adjuvants (including piperine) did not significantly raise the AUC over native curcumin; only micelles and γ-cyclodextrin complexes did so markedly (Flory et al., 2021) DOI.

A recommended piperine amount cannot be derived from the studies. In the classic study by Shoba et al., 20 mg piperine was given with 2 g curcumin (Shoba et al., 1998) DOI. Other studies used 24 mg piperine with 4 g curcuminoids (Volak et al., 2013) DOI or 10 mg three times daily (Hussaarts et al., 2019) DOI. The amount in a given supplement is stated on its label.

Data are limited. After single doses of 500 to 12,000 mg of curcuminoid extract, 7 of 24 healthy volunteers had minimal complaints that did not appear dose-related (Lao et al., 2006) DOI. In 15 cancer patients, up to 3.6 g curcumin daily for up to 4 months caused no dose-limiting toxicity (Sharma et al., 2004) DOI. These studies do not allow statements about missing extra benefit or about complaint rates above 1,500 mg.

There are no robust studies on interactions with other supplements regarding curcumin absorption. The formulation seems to be decisive: in a cross-over trial in 12 healthy adults, mainly better post-digestive solubility raised absorption, whereas strategies such as an added bioenhancer (e.g. piperine) remained ineffective (Flory et al., 2021) DOI. If you take medication, talk to your doctor first.

Read further

Want to go deeper into the subject? Here's where to continue:

Side effects: Everything on gastrointestinal side effects, safety data and interactions.
Intake guide: Information on absorption, bioavailability and different formulations.
Benefits of turmeric: An overview of the diverse health properties.

References

[1] Shoba, G. et al. (1998). Influence of piperine on the pharmacokinetics of curcumin in animals and human volunteers. Planta Medica, 64(4):353–356. DOI: 10.1055/s-2006-957450
[2] Gurley, B. J. et al. (2026). Formulation-dependent dissolution and bioaccessibility of curcuminoids and (S)-ar-turmerone from eight commercial turmeric extract- and curcumin-containing dietary supplements. Pharmaceutical Biology, 64(1):334–350. DOI: 10.1080/13880209.2026.2631826
[3] Rak, K. et al. (2026). Food Matrix as a Modulator of Spice Phytochemical Bioactivity: Evidence from In Vitro, Animal, and Human Studies. Nutrients, 18(18):3048. DOI: 10.3390/nu18183048
[4] Shamsi, S. et al. (2017). Curcumin, Piperine, and Capsaicin: A Comparative Study of Spice-Mediated Inhibition of Human Cytochrome P450 Isozyme Activities. Drug Metabolism and Disposition, 45(1):49–55. DOI: 10.1124/dmd.116.073213
[5] Lao, C. D. et al. (2006). Dose escalation of a curcuminoid formulation. BMC Complementary and Alternative Medicine, 6:10. DOI: 10.1186/1472-6882-6-10
[6] Sharma, R. A. et al. (2004). Phase I clinical trial of oral curcumin: biomarkers of systemic activity and compliance. Clinical Cancer Research, 10(20):6847–6854. DOI: 10.1158/1078-0432.CCR-04-0744
[7] Laval, J. et al. (2026). Safety assessment and gastrointestinal tolerance of a novel highly bioavailable turmeric extract formulation: A randomised, double-blind, placebo controlled clinical trial. Toxicology Reports, 16:102176. DOI: 10.1016/j.toxrep.2025.102176
[8] Akhtar, N. et al. (2026). Rarely reported cases of hepatotoxicity associated with turmeric- and curcuminoid-containing dietary supplements: a comprehensive review by USP. Pharmaceutical Biology, 64(1):866–901. DOI: 10.1080/13880209.2026.2693375
[9] European Medicines Agency, HMPC (2018). European Union herbal monograph on Curcuma longa L., rhizoma (EMA/HMPC/329755/2017), adopted 25 September 2018. ema.europa.eu

Curcumin can make the gall-bladder contract [1]; the EMA advises against turmeric medicines in biliary and liver disease and during pregnancy and breastfeeding [2]. With a tendency to kidney stones, before surgery and on blood thinners, medical advice is sensible.

In short

Gallstones, biliary and liver disease: not recommended per the EMA monograph
Pregnancy and breastfeeding: not recommended, too little data
Tendency to kidney stones: turmeric supplements raised urinary oxalate
Surgery and blood thinners: discuss with a doctor
Applies mainly to supplements, not to spice amounts in food

What's behind it

The caution concerns turmeric supplements and extracts. The reasons are effects on bile and liver, the oxalate content and missing safety data for certain groups.

What the sources show

Bile: In 12 healthy volunteers, a single 20 mg dose of curcumin reduced gall-bladder volume by up to 29 % within 2 hours compared with placebo; the authors conclude that curcumin induces contraction of the gall-bladder [1]. Because of possible stimulation of bile secretion, the EMA monograph does not recommend turmeric in obstruction of the bile duct, cholangitis, liver disease, gallstones and other biliary diseases [2].

Pregnancy and breastfeeding: According to the EMA, safety has not been established; use is not recommended for lack of data, nor for children and adolescents under 18 [2]. LactMed (NIH) reports no data on the excretion of turmeric components into breast milk [3].

Liver: A review by the US Pharmacopeia (USP) summarises that rare cases of liver injury have been reported with turmeric or curcuminoid supplements, typically 1 to 4 months after starting and generally resolving after discontinuation. The USP recommends a cautionary statement to consult a health-care practitioner beforehand with a history of liver problems [4]. In a phase I study of 15 cancer patients, 0.45 to 3.6 g curcumin daily for up to four months showed no dose-limiting toxicity [5].

Kidneys: In 11 healthy people, turmeric supplements increased urinary oxalate excretion (91 % of the oxalate in turmeric is water-soluble). This could raise the risk of kidney stones in susceptible individuals [6].

Surgery and blood thinners: A review of supplements lists curcumin among substances that may increase bleeding risk in combination with antithrombotic therapy [7]. No study defines a stopping time before surgery for turmeric itself; in general, a JAMA review calls on physicians to ask about and document herbal medication use before procedures [8]. More on blood thinners: interactions.

What this means in practice

With gallstones, biliary or liver disease, a tendency to kidney stones, pregnancy and breastfeeding, before surgery and under blood thinners, a conversation with a doctor or pharmacist is sensible before taking turmeric supplements. Tell the care team about all supplements before planned procedures. With abdominal pain, dark urine or yellowing of skin or eyes, stop taking it and seek medical advice [4].

Limits of the statement

The gall-bladder studies are small single-dose studies in healthy people. There are no intervention studies on turmeric for pregnancy, breastfeeding or surgery. The liver data come largely from case reports. This answer does not replace medical advice.

Common follow-up questions

In a small study of 12 healthy volunteers, gall-bladder volume fell by about 29% within 2 hours after 20 mg curcumin (Rasyid & Lelo, 1999) DOI. Because of possible stimulation of bile secretion, the EMA does not recommend turmeric in bile duct obstruction, gallstones and other biliary diseases (EMA, 2018) EMA/HMPC/329755/2017. Talk to your doctor first.

To our knowledge there is no study on when to stop turmeric before surgery. The EMA assessment report describes an inhibitory effect on platelets in laboratory experiments; possible interactions with antiplatelet agents are based mainly on in vitro, animal and case-report data (EMA, 2018) EMA/HMPC/749518/2016. LactMed notes an increased bleeding risk with warfarin and antiplatelet drugs (LactMed, NIH) PMID 30000906. Tell the treatment team about all supplements before procedures (Ang-Lee et al., 2001) DOI.

In the laboratory, curcumin inhibits the enzymes CYP2C9 and CYP3A4 (EMA, 2018) EMA/HMPC/749518/2016. There are individual case reports of raised INR with turmeric, for example with the vitamin K antagonist fluindione (Daveluy et al., 2014) DOI. In a study of 8 healthy volunteers, however, 4 g curcuminoids plus piperine over 2 days did not meaningfully change the metabolism of flurbiprofen (a CYP2C9 probe drug) (Volak et al., 2012) DOI. LactMed notes an increased bleeding risk (LactMed, NIH) PMID 30000906. Talk to your doctor beforehand.

The EMA does not recommend turmeric in liver disease, bile duct obstruction or other biliary diseases (EMA, 2018) EMA/HMPC/329755/2017. There are also case reports of liver injury: ten cases were collected in the USA, mostly 1 to 4 months after starting (Halegoua-DeMarzio et al., 2023) DOI. A US expert committee regards them as very rare and advises consulting a doctor if you have a history of liver problems (Akhtar et al., 2026) DOI. Discuss intake with your doctor.

The evidence is limited. The EMA states that safety during pregnancy and lactation has not been established and, in the absence of data, use is not recommended (EMA, 2018) EMA/HMPC/329755/2017. LactMed (NIH) reports no data on excretion into breast milk; turmeric as a food ingredient is regarded as GRAS in the USA (LactMed, NIH) PMID 30000906. Talk to your doctor or midwife, especially about extracts.

Side effects: A detailed look at the safety profile, side effects and interactions.
Interactions: Information on interactions with medications.
Intake guide: Intake, bioavailability and formulations.
Effects overview: General questions about effects and areas of use in research.

References

[1] Rasyid, A. & Lelo, A. (1999). The effect of curcumin and placebo on human gall-bladder function: an ultrasound study. Alimentary Pharmacology & Therapeutics, 13(2):245–249. DOI: 10.1046/j.1365-2036.1999.00464.x
[2] European Medicines Agency, HMPC (2018). European Union herbal monograph on Curcuma longa L., rhizoma (EMA/HMPC/329755/2017), adopted 25 September 2018. ema.europa.eu
[4] Akhtar, N. et al. (2026). Rarely reported cases of hepatotoxicity associated with turmeric- and curcuminoid-containing dietary supplements: a comprehensive review by USP. Pharmaceutical Biology, 64(1):866–901. DOI: 10.1080/13880209.2026.2693375
[5] Sharma, R. A. et al. (2004). Phase I clinical trial of oral curcumin: biomarkers of systemic activity and compliance. Clinical Cancer Research, 10(20):6847–6854. DOI: 10.1158/1078-0432.CCR-04-0744
[6] Tang, M., Larson-Meyer, D. E. & Liebman, M. (2008). Effect of cinnamon and turmeric on urinary oxalate excretion, plasma lipids, and plasma glucose in healthy subjects. The American Journal of Clinical Nutrition, 87(5):1262–1267. DOI: 10.1093/ajcn/87.5.1262
[3] National Institute of Child Health and Human Development (2006–). Turmeric. In: Drugs and Lactation Database (LactMed®). Bethesda (MD). PMID: 30000906; ncbi.nlm.nih.gov/books/NBK501846
[8] Ang-Lee, M. K., Moss, J. & Yuan, C.-S. (2001). Herbal medicines and perioperative care. JAMA, 286(2):208–216. DOI: 10.1001/jama.286.2.208
[7] Dobre, M.-Z. et al. (2025). Navigating the Effects of Anti-Atherosclerotic Supplements and Acknowledging Associated Bleeding Risks. International Journal of Molecular Sciences, 26(20):10183. DOI: 10.3390/ijms262010183

A randomised trial in 200 women with PCOS gave metformin and nanocurcumin alone and combined; the combination improved metabolic values more [1]. In diabetic patients on metformin, blood glucose and HbA1c did not change after 10 days of a curcumin product [2]. Medical advice is sensible.

In short

PCOS trial (n = 200, 12 weeks): metformin plus nanocurcumin improved glucose and lipid values more than either alone
Diabetic patients on metformin: 10 days of a curcumin product, no change in blood glucose/HbA1c
No pharmacokinetic interaction study of metformin and curcumin found
Have blood glucose monitored by a doctor when combining

What's behind it

Metformin and curcumin are both associated with glucose metabolism, which is why the combination is studied. Direct studies are rare.

What the sources show

Combination trial in PCOS: In a randomised, double-blind, placebo-controlled trial (Feghhi et al., 2024), 200 women with polycystic ovary syndrome (PCOS) received, for 12 weeks, metformin (500 mg every 8 hours), nanocurcumin soft gel capsules (80 mg every 8 hours), both, or placebo. The combination improved lipid values, glucose metabolism markers, hormone levels, body weight and BMI more than the single substances or placebo [1]. The study concerns a specific nano-formulation and a specific group of patients.

Compatibility with metformin: In an observation of diabetic patients on metformin, blood glucose and HbA1c were measured before and after 10 days of a curcumin-phospholipid product (Meriva®); no interactions with the metformin therapy were observed [2]. The period is short.

Curcumin and glucose values in general: A systematic review of 20 randomised trials of curcumin plus piperine (duration 1 to 12 weeks, curcumin 500–1,500 mg daily) found decreases in fasting glucose, HbA1c and HOMA-IR in people with metabolic syndrome and type 2 diabetes [3]. In a study of 240 people with prediabetes, after 9 months no one in the curcumin group but 16.4 % of the placebo group was diagnosed with type 2 diabetes; HOMA-IR was lower in the curcumin group [4]. These studies examined curcumin without metformin; they say nothing about the combination.

General caution: A review of pharmacokinetic interactions concludes that the data are insufficient for clinical judgement and advises caution with combinations of curcumin and drugs [5].

What this means in practice

Anyone taking metformin is well advised to discuss curcumin products beforehand with the treating doctor and to continue blood glucose monitoring as agreed. With symptoms such as trembling, sweating or ravenous hunger, seek medical advice. More in the blood sugar hub.

Limits of the statement

The combination trial concerns women with PCOS and a nano-formulation; the observation in diabetic patients lasted 10 days. Studies on metformin combined with curcumin as a spice are lacking. This answer does not replace medical advice.

Common follow-up questions

Two studies in women with PCOS examined the combination. In a 12-week trial (200 women; metformin 500 mg and nanocurcumin 80 mg every 8 hours), markers of glucose metabolism, blood lipids, testosterone and weight improved more than with the single agents or placebo (Feghhi et al., 2024) DOI. In another study (100 women, 3 months), fasting insulin, HOMA-IR and testosterone were lower when 80 mg/day nanomicelles were added to metformin than with metformin alone (Sohrevardi et al., 2021) DOI. Whether this applies to other groups is open.

This cannot be judged reliably from the studies. A review describes curcumin as well tolerated in clinical trials, with occasional gastrointestinal complaints (Soleimani et al., 2018) DOI. We found no studies on interactions specifically with metformin; the two PCOS studies of the combination report no safety data in their abstracts (Feghhi et al., 2024) DOI (Sohrevardi et al., 2021) DOI. If you take metformin, talk to your doctor first.

In two studies in women with PCOS, markers of insulin resistance improved more with metformin plus curcumin than with metformin alone (Sohrevardi et al., 2021) DOI (Feghhi et al., 2024) DOI. We found no human pharmacokinetic studies on whether curcumin changes metformin absorption or levels, so no statement on a mechanism is possible.

You should discuss this with your treating doctor, especially because blood glucose values may be affected. The data are limited: mainly two studies of 12 weeks and 3 months in women with PCOS (Feghhi et al., 2024) DOI (Sohrevardi et al., 2021) DOI; we found no pharmacokinetic data for the combination.

Keep reading

Want to go deeper? Here's where to continue:

Side effects: All gastrointestinal side effects, safety data and interactions in detail.
Interactions: Detailed information on interactions with medications.
Blood sugar hub: Everything on diabetes, insulin resistance and glucose metabolism.

References

[1] Feghhi, F. et al. (2024). Effects of metformin and curcumin in women with polycystic ovary syndrome: A factorial clinical trial. Phytomedicine, 135:156160. DOI: 10.1016/j.phymed.2024.156160
[2] Hu, S. et al. (2018). Interaction study between antiplatelet agents, anticoagulants, thyroid replacement therapy and a bioavailable formulation of curcumin (Meriva®). European Review for Medical and Pharmacological Sciences, 22(15):5042–5046. DOI: 10.26355/eurrev_201808_15647
[3] Pan, C. et al. (2026). Curcumin-piperine supplementation modulates inflammation, oxidative stress, and cardiometabolic risk: a systematic review of randomized controlled trials. Frontiers in Nutrition, 13:1814168. DOI: 10.3389/fnut.2026.1814168
[4] Chuengsamarn, S. et al. (2012). Curcumin extract for prevention of type 2 diabetes. Diabetes Care, 35(11):2121–2127. DOI: 10.2337/dc12-0116
[5] Bahramsoltani, R., Rahimi, R. & Farzaei, M. H. (2017). Pharmacokinetic interactions of curcuminoids with conventional drugs: A review. Journal of Ethnopharmacology, 209:1–12. DOI: 10.1016/j.jep.2017.07.022

In breast cancer patients, curcumin lowered active tamoxifen levels [1], and in cell and mouse models it weakened the effect of some chemotherapy drugs [2]. Turmeric supplements should therefore only be taken after consulting the oncologist. It does not replace cancer therapy.

In short

Patients on tamoxifen: curcumin (+/- piperine) lowered endoxifen levels by 8–12 %
Cell and mouse models: curcumin inhibited the effect of camptothecin, doxorubicin and cyclophosphamide
Review: antioxidant supplements are best avoided during chemo-/radiotherapy
Always coordinate with the oncology team
Not a replacement for cancer therapy

What's behind it

Curcumin can influence drugs via enzymes and transporters, and it has antioxidant activity. Both matter in chemotherapy because some cytotoxic drugs act via oxidative stress or are processed by liver enzymes.

What the sources show

Tamoxifen: In a study of breast cancer patients, women took tamoxifen alone or together with curcumin (1,200 mg three times daily), partly with piperine. Exposure to the active metabolite endoxifen fell by 7.7 % with curcumin (not significant) and by 12.4 % with curcumin plus piperine (significant). The authors consider it possible that endoxifen levels fall below the efficacy threshold in some patients [1].

Cell experiments and mouse model: In breast cancer cell lines, curcumin inhibited apoptosis induced by camptothecin, mechlorethamine and doxorubicin by up to 70 %. In mice with human breast tumours, dietary curcumin reduced tumour regression under cyclophosphamide. The authors suggest examining whether breast cancer patients undergoing chemotherapy should avoid curcumin [2].

Tolerability in cancer: In a phase II trial, 25 patients with advanced pancreatic cancer took 8 g of curcumin daily; no toxicities were observed, and the compound was found only at low levels in blood [3]. This study did not examine interaction with chemotherapy.

Antioxidants in general: A review of randomised trials in the Journal of the National Cancer Institute concludes that antioxidant supplements during chemotherapy and radiotherapy should be discouraged because of possible tumour protection and reduced survival. Some trials, in contrast, found fewer treatment side effects [4].

General caution: A review of pharmacokinetic interactions names cytotoxic agents alongside cardiovascular drugs, anticoagulants, antibiotics and others as affected drug classes; the data were not enough to judge clinical interactions reliably, and the authors advise caution [5].

What this means in practice

Anyone receiving cancer therapy should discuss every supplement, including turmeric, with the oncology team beforehand. This applies especially to extracts and to tamoxifen. The sources contain no studies of turmeric as a kitchen spice in usual amounts during chemotherapy. Curcumin does not replace oncological therapy.

Limits of the statement

The indications of weakened chemotherapy come from cell culture and mouse models; the tamoxifen study is small and involves high curcumin doses. For other cytotoxic drugs, the sources contain no human data. This answer does not replace oncological advice.

Common follow-up questions

In laboratory and animal studies, curcumin inhibits cytochrome P450 enzymes and the transporter P-glycoprotein and can thereby change the blood levels of some drugs, including chemotherapeutics. There are hardly any clinical studies; the evidence is not sufficient for a clinical judgement (Bahramsoltani et al., 2017) DOI. Discuss any intake with your oncology team beforehand.

Whether antioxidant supplements weaken chemotherapy is disputed: a review advises against them because of possible tumour protection and reduced survival, but admits conflicting data (Lawenda et al., 2008) DOI. In a breast cancer study (n = 1,134), antioxidant use (vitamins A, C, E, carotenoids, Q10) tended to go with a higher risk of recurrence (HR 1.41; 95% CI 0.98–2.04; not significant); curcumin was not examined (Ambrosone et al., 2019) DOI. For curcumin itself, a review describes rather protective effects on healthy tissue (Liu et al., 2018) DOI. Increased toxicity from curcumin is therefore not proven.

Only after consulting your oncology team. For antioxidant supplements during chemotherapy and radiotherapy, a review article recommended avoiding them (Lawenda et al., 2008) DOI. For curcumin, interactions with chemotherapeutics are possible but hardly studied clinically (Bahramsoltani et al., 2017) DOI.

According to a review, curcumin inhibits CYP isoenzymes that break down many drugs, as well as P-glycoprotein (Bahramsoltani et al., 2017) DOI. The EMA assessment report lists CYP2C9 and CYP3A4 as strongly and CYP2B6, CYP1A2 and CYP2D6 as moderately inhibited in laboratory tests (IC50 4.3–50.3 µM) (EMA, 2018) EMA.

Interactions & Safety

How does turmeric interact with blood thinners?

What's behind it

What the sources show

What this means in practice

Limits of the statement

Common follow-up questions

Does curcumin have an influence on blood clotting?

Is curcumin a blood thinner?

Can you take warfarin together with curcumin?

Which medications besides blood thinners are affected?

When should you seek medical advice?

Read more

References

Can turmeric be used on open wounds?

What's behind it

What the sources show

What this means in practice

Limits of the statement

Common follow-up questions

How well does turmeric heal wounds?

Can you sprinkle turmeric powder on open wounds?

Does curcumin help with diabetic wounds?

Is curcumin effective orally for wound healing?

How long does wound healing with curcumin take?

Read further

References

Can taking turmeric affect fertility?

What's behind it

What the sources show

What this means in practice

Limits of the statement

Common follow-up questions

Can turmeric affect sperm quality?

Is turmeric safe during pregnancy?

Does curcumin affect hormones?

Further reading

References

What should you avoid when taking turmeric/curcumin?

What's behind it

What the sources show

What this means in practice

Limits of the statement

Common follow-up questions

Does piperine always help with absorption?

How much piperine should I take?

What happens at high doses over 1,500 mg?

Can I take curcumin with other supplements?

Read further

References

When should you not take turmeric?

What's behind it

What the sources show

What this means in practice

Limits of the statement

Common follow-up questions

Why should turmeric be avoided with gallstones?

How long before an operation should turmeric be paused?

What about blood thinners?

Is turmeric a concern with liver diseases?

May turmeric be taken during pregnancy or breastfeeding?

Read more

References

Can metformin be taken together with turmeric?

What's behind it

What the sources show

What this means in practice

Limits of the statement

Common follow-up questions

Does curcumin help metformin patients?

Is the combination safe?

Can curcumin affect the effect of metformin?

Should I take curcumin with metformin?

Keep reading

References

Why no turmeric during chemotherapy?

What's behind it

What the sources show

What this means in practice

Limits of the statement