Advising patients using turmeric on its potential interactions

Alex Bailey, Information Specialist, Welsh Medicines Information CentrePublished

Turmeric and its main active constituent, curcumin, have the potential to interact with conventional medicines and other herbal supplements.

General interactions considerations

  • Information on turmeric’s interactions with conventional medicines is limited and comes mostly from in vitro (test tube) or animal studies so may not be clinically relevant in humans.
  • Use caution when taking medicinal doses of turmeric or curcumin at the same time as medicines with significant side effects (e.g. anticancer or immunosuppressant agents) or medicines with a narrow therapeutic index.
  • Small changes in the dose can have a large effect and may result in unacceptable adverse effects for medicines with a narrow therapeutic index like warfarin, lithium, digoxin and phenytoin.

Interactions with specific medicines or groups of medicines

The following section provides advice and guidance on actions to take for medicines known to interact with turmeric.

Anticoagulants or antiplatelets

The risk of bleeding might be increased because turmeric may interfere with clotting by decreasing platelet aggregation.

Use caution when turmeric or curcumin are taken with medicines or supplements that have anticoagulant or antiplatelet (blood thinning) effects.

Warfarin

  • Curcumin might decrease the clearance of warfarin from the body.
  • Monitor closely if warfarin and curcumin are taken together, especially as warfarin has a narrow therapeutic index (where there is a small difference between being clinically effective and causing toxicity).
  • Raised international normalised ratio (INR) to a level associated with a serious risk of bleeding was reported in a person taking warfarin who also started to take a product containing turmeric. The person’s INR measurements had previously been stable and the reporter considered that turmeric in the product this person took had interacted with warfarin.

Clopidogrel

  • In an animal study, the amount of clopidogrel in the bloodstream was significantly increased when curcumin was taken at a high dose (100 mg/kg) for seven days.

Herbal supplements

Supplements that might have anticoagulant or antiplatelet effects include:

  • angelica
  • clove
  • danshen
  • garlic
  • ginkgo
  • ginger
  • Panax ginseng
  • willow

Antidiabetic medicines

Turmeric or curcumin might reduce blood glucose and increase the risk of hypoglycaemia (low blood sugar).

If a person has diabetes or takes herbal supplements that could reduce blood glucose levels, advise them to let their healthcare professional (e.g. doctor, nurse or pharmacist) know that they intend to take turmeric or curcumin before they start.

Glyburide

  • In a study in eight people with type 2 diabetes who were taking glyburide 5 mg, curcumin was added in for 10 days. On day 11, their blood glucose levels remained significantly lower for 24 hours than they had been before the curcumin was started.

Herbal supplements

Supplements that could reduce blood glucose levels include:

  • eleuthero (Siberian ginseng)
  • fenugreek
  • garlic
  • guar gum
  • horse chestnut
  • Panax ginseng
  • psyllium

Chemotherapy

Taking turmeric or curcumin while you are undergoing cancer chemotherapy treatment is not recommended.

Curcumin might alter the effect of chemotherapy medicines.

Doxorubicin, cyclophosphamide, paclitaxel, docetaxel

  • There is evidence that curcumin affects tumour initiation and progression at a molecular level.
  • Turmeric might reduce or increase the cytotoxic efficacy (ability to prevent cell growth and replication) of doxorubicin and cyclophosphamide, depending on the dose used.
  • Curcumin might increase the bioavailability of paclitaxel and docetaxel.

Everolimus

  • One animal study suggests that curcumin might reduce everolimus levels.

Medicines metabolised by CYP450 enzymes

Use caution when taking turmeric or curcumin at the same time as conventional medicines that are metabolised (broken down) by these enzymes.

Curcumin might affect some CYP450 enzymes but evidence in humans to support this is lacking.

Medicines metabolised by CYP1A1, CYP1A2, CYP2A6, CYP2B6, CYO2D6, CYP2C9, CYP3A4

Free resources are available with information on medicines that are metabolised (broken down) by or affect CYP450 enzymes:

Evidence

Acute nephrotoxicity (kidney injury) and high tacrolimus levels (29 nanogram/mL) were reported and attributed to turmeric in a person who had taken “15 or more spoonfuls” of turmeric powder daily for ten days before the high tacrolimus levels were recorded. The case report therefore describes evidence of turmeric moderately inhibiting CYP3A4.

Hormone replacement therapy (HRT)

Use caution when taking turmeric or curcumin with HRT:

  • Theoretically, curcumin in large amounts could interfere with HRT by competing for oestrogen receptors.
  • In vitro (test tube) research shows that curcumin can displace oestrogen from its receptors.

Loratadine, losartan, midazolam and verapamil

  • Turmeric might raise levels of these medicines by inhibiting P-glycoprotein, which transports medicines out of cells.

Evidence

Raised concentrations of loratadine, losartan, midazolam and verapamil were seen in animal and in vitro (test tube) studies with turmeric constituents.

In one study, eight healthy adults took a piperine-containing curcumin preparation for two days. Following a subsequent single 3 mg dose of midazolam, there was increased exposure to the main active breakdown product of midazolam, but not to midazolam itself.

Norfloxacin

  • Turmeric might increase blood levels of norfloxacin.

Evidence

One animal study suggested that pre-treatment with curcumin could raise the levels of norfloxacin in the blood.

Statins

  • Use statins cautiously with turmeric because the products turmeric breaks down into could increase statin blood levels.
  • This might lead to increased adverse effects, including myopathy (muscle weakness and/or pain), which is dose-dependent.

Evidence

Levels of rosuvastatin were increased in animal studies with turmeric, possibly due to the action of curcumin breakdown products. Other statins might be affected similarly.

Sulfasalazine

  • Curcumin might increase the blood levels and adverse effects of sulfasalazine.

Evidence

Sulfasalazine plasma concentrations were 3.2 times higher when sulfasalazine was taken at the same time as a 2 g daily dose of curcumin in a small study of 8 people.