Supplement and drug interactions: CoQ10, St John's wort, turmeric and the combinations to check

Short answer

Supplements can interact with prescription medicines. Some change how a medicine is absorbed or broken down, and some add to or work against its effect. These are the combinations that US government health sources name most clearly:

• St John's wort. According to the National Center for Complementary and Integrative Health (NCCIH), it can weaken the effects of many medicines, including birth control pills, warfarin, certain statins, cyclosporine, some heart, seizure, HIV and cancer drugs and some antidepressants, and with certain antidepressants it may lead to serious serotonin-related side effects (NCCIH).

• CoQ10. NCCIH says it may interact with the blood thinner warfarin and with insulin, and may not be compatible with some types of cancer treatment (NCCIH).

• Blood thinners. NCCIH says ginkgo and garlic supplements may increase the risk of bleeding (NCCIH ginkgo, NCCIH garlic); NIH's Office of Dietary Supplements (ODS) lists large doses of vitamin E as raising bleeding risk with anticoagulant or antiplatelet medicines (ODS) and says fish oil might raise INR with warfarin (ODS).

• Vitamin K and warfarin. ODS says people taking warfarin need a consistent intake of vitamin K from food and supplements (ODS).

• Thyroid tablets. MedlinePlus advises taking calcium carbonate or ferrous sulfate (iron) at least 4 hours before or after levothyroxine (MedlinePlus).

• Ashwagandha. NCCIH says there is evidence it might interact with thyroid, diabetes, blood pressure, sedative, anti-seizure and immunosuppressant medicines (NCCIH).

The single most useful step is to give your pharmacist a full list of everything you take, including supplements, teas and over-the-counter products. MedlinePlus recommends keeping a written list of all your medicines, vitamins, minerals and supplements and bringing it to every visit (MedlinePlus).

If you started a supplement because you wanted to feel better and are now worried it might clash with your medicines, it is not your fault. Supplement labels rarely mention interactions, and many people are never asked about them.

Why supplements and medicines interact

The sources describe several ways a supplement can interfere with a medicine:

1. Absorption in the gut. Some minerals bind to certain medicines and reduce how much is absorbed. ODS, for example, says magnesium can form insoluble complexes with some antibiotics (ODS), and MedlinePlus gives a time gap between calcium carbonate or iron and levothyroxine (MedlinePlus).

2. Weakening a medicine. NCCIH says St John's wort can weaken the effects of many medicines, including crucially important ones (NCCIH).

3. Adding to the same effect. Examples from the sources: ginkgo and garlic with blood thinners and bleeding (NCCIH ginkgo, NCCIH garlic); chromium with diabetes medicines and low blood sugar (ODS); valerian with alcohol or sedatives (NCCIH).

4. Working against the medicine. ODS says sudden changes in vitamin K intake can increase or decrease warfarin's effect (ODS).

NCCIH notes that, unlike drugs, dietary supplements are not approved by the FDA before they are sold to the public (NCCIH). Labels often do not mention interactions, which leaves the check to you and your pharmacist.

What medications should not be taken with CoQ10?

What medications should not be taken with CoQ10 is by far the most searched interaction question. The NCCIH summary is short: CoQ10 "may interact with the anticoagulant (blood thinner) warfarin and the diabetes drug insulin, and it may not be compatible with some types of cancer treatment" (NCCIH).

• Warfarin. MedlinePlus lists coenzyme Q10 among nonprescription or herbal products that may interact with warfarin and says not to start any of them while taking warfarin without discussing it with your healthcare provider (MedlinePlus). MedlinePlus adds that your doctor may change your medicine doses or monitor you carefully for side effects.

• Insulin. NCCIH lists a possible interaction with insulin (NCCIH). If you use insulin, ask your doctor before starting CoQ10.

• Some cancer treatments. NCCIH says CoQ10 may not be compatible with some types of cancer treatment (NCCIH). Discuss any supplement with your oncology team.

CoQ10 and blood pressure medicines are often listed together online. NCCIH does not list blood pressure medicines among CoQ10's interactions, and it says the small amount of evidence available suggests CoQ10 probably doesn't have a meaningful effect on blood pressure (NCCIH). That is a statement about benefit, not evidence that the combination is right for you, so tell your doctor if you take both.

CoQ10 and statins are often taken together, in the hope of reducing statin-related muscle aches. NCCIH says the overall scientific evidence does not support the idea that CoQ10 can reduce muscle pain caused by statins (NCCIH). Tell your prescriber if you take both, and report muscle pain or weakness on a statin rather than treating it yourself.

On side effects, NCCIH says no serious side effects of CoQ10 have been reported and that mild side effects such as insomnia or digestive upsets may occur (NCCIH).

St John's wort: the supplement with the longest interaction list

St John's wort is taken for low mood. NCCIH says it "has been clearly shown" that it can interact in dangerous, sometimes life-threatening ways with a variety of medicines. According to NCCIH, it can weaken the effects of (NCCIH):

• birth control pills;

• cyclosporine, which prevents the body from rejecting transplanted organs;

• some seizure medicines, including phenytoin and carbamazepine;

• some heart medicines, including digoxin and ivabradine;

• some HIV drugs, including indinavir and nevirapine;

• some cancer medicines, including irinotecan, imatinib and docetaxel;

• warfarin;

• certain statins, including simvastatin;

• some antidepressants, including amitriptyline and bupropion.

NCCIH adds that taking St John's wort with certain antidepressants or other drugs that affect serotonin may lead to increased serotonin-related side effects, which can be serious (NCCIH). MedlinePlus lists symptoms of serotonin syndrome, including agitation or restlessness, a fast heartbeat and high blood pressure, increased body temperature, overactive reflexes, loss of coordination and diarrhea, says untreated it can be deadly, and advises contacting your provider right away if you have symptoms (MedlinePlus).

St John's wort and the pill matters because a weaker pill could lead to unplanned pregnancy. If you take or plan to take St John's wort, ask your doctor or pharmacist about your contraception.

Turmeric and blood thinners

Turmeric and blood thinners is a common search. The government sources we used do not name a turmeric–blood thinner interaction: the NCCIH turmeric fact sheet does not list specific drug interactions, and turmeric is not on the MedlinePlus warfarin page's list of products (NCCIH, MedlinePlus). That does not mean the combination has been shown to be safe. NCCIH advises talking with your health care provider before using any herbal product if you take any type of medicine, and MedlinePlus says to tell your doctor and pharmacist about all vitamins, supplements and herbal products while on warfarin, because some of them may increase the risk of bleeding (MedlinePlus).

There is a separate, documented concern. NCCIH says highly bioavailable curcumin formulations, which are made to be absorbed better, may harm your liver, and that liver damage has been reported in some people who took them (NCCIH). The NIH LiverTox entry describes reported cases as starting gradually with fatigue, nausea and poor appetite, followed by dark urine and jaundice (LiverTox). NCCIH says that if you notice symptoms such as fatigue, nausea, poor appetite, dark urine or jaundice, you should stop turmeric or curcumin products immediately and talk with your health care provider (NCCIH).

What medications should not be taken with turmeric? The sources we used do not give a list. If you take a blood thinner or any regular medicine, ask your pharmacist before starting a turmeric or curcumin supplement.

Blood thinners: the supplements to check

If you take a blood thinner, check before taking any of the products below. Most sources name warfarin specifically; ask your pharmacist how this applies to your medicine.

Vitamin K and warfarin deserve a specific note. ODS says what matters is a consistent intake of vitamin K from food and supplements, because sudden changes can increase or decrease warfarin's effect (ODS). MedlinePlus advises eating consistent amounts of vitamin K-containing food week to week, not eating large amounts of leafy green vegetables or certain vegetable oils that contain a lot of vitamin K, and talking to your doctor before changing your diet (MedlinePlus).

Fish oil and blood thinners. ODS reports that most studies found 3–6 g a day of fish oil did not significantly affect anticoagulant status in people taking warfarin, and that a 2014 review concluded omega-3s don't affect the risk of clinically significant bleeding. ODS also notes that fish oil might prolong clotting times, and that package inserts for prescription omega-3 products advise monitoring INR periodically in people taking anticoagulants (ODS). Tell the clinic that manages your blood thinner if you take fish oil.

Thyroid medicine: what not to take with levothyroxine

What not to take with levothyroxine comes up often, because several common products can affect it. According to MedlinePlus (MedlinePlus):

• Calcium carbonate (Tums) or ferrous sulfate (an iron supplement): take it at least 4 hours before or 4 hours after levothyroxine.

• Other nonprescription products that may interact include proton pump inhibitors such as omeprazole, antacids, simethicone, aspirin and other salicylates, niacin and NSAIDs such as ibuprofen; tell your doctor and pharmacist if you take them.

• Foods: soybeans, walnuts and dietary fiber may affect how levothyroxine works; talk to your doctor about these and about grapefruit.

• How it is usually taken: once a day on an empty stomach, 30 minutes to 1 hour before breakfast, with a full glass of water.

ODS adds that in a small study, chromium picolinate taken at the same time as levothyroxine reduced levothyroxine absorption (ODS).

Can you take magnesium with levothyroxine? Magnesium supplements are not named on the MedlinePlus levothyroxine page, but antacids and magnesium salicylate are among the listed products (MedlinePlus). The sources we used do not give a time gap for magnesium supplements and levothyroxine, so ask your pharmacist.

Can you take biotin with levothyroxine? The ODS biotin fact sheet does not describe an interaction with levothyroxine itself. Its concern is lab tests: very high biotin intakes may interfere with some lab assays, "even a single 10 mg dose of biotin has interfered with thyroid function tests", and, according to the FDA, one patient taking high-dose biotin died after a troponin heart test gave a falsely low result (ODS). ODS notes that the FDA advises health care providers to ask patients about supplements containing biotin, so tell whoever orders your blood tests that you take it.

Ashwagandha and thyroid medication may interact: NCCIH lists thyroid hormone medicines among possible interactions and says ashwagandha is not recommended for people with thyroid disorders (NCCIH).

Antidepressants and mood medicines

• St John's wort can weaken some antidepressants, including amitriptyline and bupropion, and with certain antidepressants may lead to serious serotonin-related side effects, according to NCCIH (NCCIH).

• SAMe, sometimes taken for mood, might interact with drugs and supplements that increase serotonin, such as antidepressants, L-tryptophan and St John's wort, according to NCCIH. NCCIH also says SAMe may decrease the effects of levodopa and may worsen symptoms of mania in bipolar disorder (NCCIH).

• Valerian should not be taken along with alcohol or sedatives, NCCIH says, because it might have a sleep-inducing effect (NCCIH).

• Ashwagandha may interact with sedatives, according to NCCIH (NCCIH).

Ask your pharmacist before combining any supplement with an antidepressant or a sedative.

Blood pressure, heart and diabetes medicines

• Potassium. ODS says ACE inhibitors, angiotensin receptor blockers and potassium-sparing diuretics such as spironolactone reduce potassium loss in urine and can cause high potassium (hyperkalemia), especially with impaired kidney function, and that some people should consult their health care provider before taking salt substitutes because of this risk (ODS). Ask your doctor before taking potassium supplements or salt substitutes with these medicines.

• Red yeast rice. NCCIH says it can contain monacolin K, which is structurally identical to the statin lovastatin, and that products with significant amounts can have the same potential side effects as statins, including muscle, kidney and liver damage, and the same types of drug interactions (NCCIH). Tell your doctor if you take it, especially alongside a prescribed statin.

• Niacin. ODS says large doses of nicotinic acid can raise blood sugar, so people on diabetes medicines who take high doses should have their blood glucose monitored. In a large trial cited by ODS, adding extended-release nicotinic acid to a statin did not reduce major vascular events and raised the risk of diabetes, stomach upset and diarrhea (ODS).

• Chromium. ODS says chromium might increase insulin sensitivity and may have an additive effect with insulin, metformin and other diabetes medicines, which might increase the risk of low blood sugar (ODS).

• Milk thistle. NCCIH reports that a small number of studies suggest milk thistle extracts may help control blood sugar in type 2 diabetes (NCCIH); if you take diabetes medicines, tell your doctor before using it.

• Ashwagandha may interact with diabetes and blood pressure medicines, according to NCCIH (NCCIH).

• Licorice root. NCCIH says its glycyrrhizin can cause serious adverse effects such as irregular heartbeat and cardiac arrest, that even small amounts have been linked to severe effects in people with high blood pressure or heart or kidney conditions, and that interactions with corticosteroids have been reported (NCCIH).

Antibiotics, osteoporosis medicines and magnesium

• Tetracycline and quinolone antibiotics (such as doxycycline, ciprofloxacin and levofloxacin): ODS says magnesium can form insoluble complexes with them and that these antibiotics should be taken at least 2 hours before or 4 to 6 hours after a magnesium-containing supplement (ODS).

• Oral bisphosphonates for osteoporosis (such as alendronate): ODS says magnesium-rich supplements or medications can reduce their absorption and that taking them at least 2 hours before or after the bisphosphonate minimizes the interaction (ODS).

For other minerals and other antibiotics, ask your pharmacist for the gap that applies to you.

Milk thistle, CBD, melatonin and other popular products

What medications should not be taken with milk thistle? NCCIH does not name specific drug interactions. It notes that milk thistle may help control blood sugar in type 2 diabetes, so it may matter if you take diabetes medicines, and it advises talking with your health care provider before using milk thistle if you take any medicine (NCCIH).

What drugs should not be taken with CBD? According to the FDA, taking CBD with other medications may increase or decrease the effects of those medications, which may lead to more side effects or reduced effectiveness; CBD can cause liver injury; and using it with alcohol or other drugs that slow brain activity, such as those for anxiety, panic, stress or sleep, increases the risk of sedation and drowsiness, which can lead to injuries. The FDA also says it tested some products and many did not contain the levels of CBD they claimed (FDA). Ask your pharmacist about your specific medicines.

Melatonin. NCCIH says people who take medicine should consult their health care providers before using melatonin, and that people with epilepsy and those taking blood thinners need to be under medical supervision when taking it (NCCIH).

How to check your own combination

1. Make a complete list: prescriptions, over-the-counter medicines, vitamins, minerals, herbs, teas, CBD and "natural" products, with doses. MedlinePlus recommends carrying such a list and bringing it to every visit (MedlinePlus).

2. Bring it to your pharmacist, not just your doctor. Pharmacists check interactions as part of their job.

3. Ask about timing, not just yes or no. Some sources give time gaps for specific combinations, such as calcium or iron and levothyroxine, or magnesium and some antibiotics.

4. Tell every prescriber about your supplements, especially before surgery, chemotherapy or a new medicine.

5. Note the date whenever you start or stop a supplement, so you can tell your pharmacist exactly what changed.

Living with medicines and supplements: the questions people ask next

Can I take CoQ10 with blood pressure medication?

Ask your doctor or pharmacist first. NCCIH does not list blood pressure medicines among CoQ10's interactions and says CoQ10 probably doesn't have a meaningful effect on blood pressure (NCCIH). That is not evidence the combination is right for you. The interactions NCCIH does list are with warfarin and insulin.

Is turmeric safe with blood thinners?

The government sources we used neither list a turmeric–blood thinner interaction nor say the combination is safe. MedlinePlus advises telling your doctor about all herbal products while on warfarin, because some may increase bleeding risk, and NCCIH says highly bioavailable curcumin products may harm the liver (MedlinePlus, NCCIH). Ask the clinic that manages your blood thinner before taking turmeric supplements.

Can I take St John's wort with birth control?

Talk to your doctor or pharmacist first. NCCIH says St John's wort can weaken the effects of birth control pills (NCCIH), which could lead to unplanned pregnancy. Ask them what that means for your contraception.

Should I stop supplements before surgery?

Tell your surgical team everything you take, and follow their instructions on what to stop and when. NCCIH says it is especially important to tell your providers about garlic supplements if you are going to have surgery, because they may increase bleeding, and that ashwagandha is not recommended for people about to have surgery (NCCIH garlic, NCCIH ashwagandha).

Do supplements interact with antidepressants?

The best-documented concerns in the sources are St John's wort, which can weaken some antidepressants and cause serotonin-related side effects, and SAMe, which might interact with antidepressants and with L-tryptophan (NCCIH, NCCIH). Ask your pharmacist before combining anything with an antidepressant.

Can I take supplements during chemotherapy?

Discuss every supplement with your oncology team before and during treatment. NCCIH says CoQ10 may not be compatible with some types of cancer treatment and that St John's wort can weaken some cancer medicines, including irinotecan, imatinib and docetaxel (NCCIH, NCCIH).

Before you blame yourself

If you have been taking a supplement alongside a medicine and only now learned they might interact, it is not a personal failure. Supplement bottles rarely carry warnings, appointments are short, and nobody asked. Telling your pharmacist now is the step that helps.

The habit that protects you is simple: tell your pharmacist everything you take, every time something changes.

When to see a doctor

Talk to your doctor or pharmacist before starting any supplement if you take blood thinners, thyroid medicine, antidepressants, seizure medicines, transplant medicines, HIV medicines, diabetes medicines, heart medicines or cancer treatment, or if you are pregnant or breastfeeding.

If you take warfarin, MedlinePlus says to call your doctor immediately for symptoms including bleeding that won't stop, nosebleeds, bleeding gums, coughing or throwing up blood or material that looks like coffee grounds, easy bruising, pink, red or dark brown urine, red or tarry black bowel movements, headache, dizziness or weakness (MedlinePlus). MedlinePlus advises contacting your provider right away if you have symptoms of serotonin syndrome (MedlinePlus). NCCIH says to stop turmeric or curcumin products and talk with your provider if you notice signs of liver damage such as dark urine or jaundice (NCCIH).

In an emergency: if someone has collapsed, had a seizure, has trouble breathing or can't be woken up, call 911 right away. If you think too much of a medicine has been taken, call Poison Control at 1-800-222-1222 — a free, confidential line that connects you to your local poison center, 24 hours a day (MedlinePlus, HRSA Poison Help).

How to bring this up with your doctor

What to ask for, by name. "Could you check all my medicines and supplements for interactions?" If you take warfarin: "Should my INR be checked if I start or stop this supplement?"

What to bring. Every product, ideally in its original packaging or with a photo of the label showing ingredients and amounts per serving.

What to say, out loud. "I take [supplement] for [reason]. Does it interact with [medicine], and if I can take both, how should I time them?"

If you're told to just stop all supplements. Ask: "Which one is the problem, and is there a way to time it or an alternative?"

How long until you notice a difference? Most supplements take weeks, not days. See how long supplements take to work, and how to tell if one is working.

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How Welltory helps — and what it cannot do

The limits first. Welltory is a general wellness product, not a medical device. It cannot check interactions, measure drug levels or diagnose any condition. Your pharmacist checks interactions.

What it can do is help you notice changes after you start or stop something, so you can report specifics.

Mark every change. On the Today screen (iOS, with Apple Watch or Oura), when Welltory marks a stress or rest episode and asks "What happened?", tap, type or talk: "started CoQ10", "stopped St John's wort", "new statin". Over weeks, My Patterns shows which tags tend to appear with stress and recovery; some sections need a paid plan.

Watch sleep and heart rate. Sleep Analysis uses Apple Watch or Oura data on iOS and syncs sleep from Samsung Health, Fitbit or Garmin Connect through Health Connect on Android (Sleep Analysis for Android). On the Today screen (iPhone with Apple Watch or Oura), Battery starts each morning from your resting heart rate on waking and your sleep (Today screen). An unusual change in resting heart rate or sleep after starting a new product is worth mentioning. Welltory does not alert you to an interaction.

A record for your doctor. From the web app you can export a CSV (Dashboard → choose a chart → Export) (export guide). Patterns are associations to discuss with your doctor, not proof of an interaction.

How we made it

We based this article only on US government sources: NCCIH fact sheets for St John's wort, CoQ10, turmeric, ginkgo, garlic, ashwagandha, milk thistle, red yeast rice, SAMe, licorice root, valerian and melatonin; NIH Office of Dietary Supplements fact sheets for vitamin K, vitamin E, omega-3 fatty acids, magnesium, potassium, biotin, niacin and chromium; MedlinePlus pages on levothyroxine, warfarin, serotonin syndrome and poisoning first aid; the NIH LiverTox entry for turmeric; FDA consumer information on CBD; and the HRSA Poison Help page. Every source was opened again on October 21, 2026, and statements we could not match to one of these sources were removed. This article has not been reviewed by a clinician. Search questions came from what people in the United States most often ask about supplement and medicine interactions. For the product section, we checked every function against the Welltory Help Center on October 21, 2026.

Made with AI tools, then edited and fact-checked by the Welltory team. See our Editorial & AI policy.

Jane Smorodnikova, co-founder of Welltory, built the methodology behind how we read physiological data.

Written by Tatsiana Yashyna.

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