Drug-Supplement Interactions*

Many prescription medication users in the U.S. are taking their medication in combination with a natural supplement. There are numerous different potential drug-supplement interactions. The interactions related to some of the most commonly used supplements are described in the following table. Each interaction below is rated based on the potential severity of the interaction as follows:

Despite these general classifications, it is important to understand that different people respond differently to medications and supplements. It is possible that certain interactions will occur in some people, but not others.

Supplement Medication(s) Rating Comments
Ashwagandha Thyroid hormones Moderate Ashwagandha might increase thyroid hormone levels. Taking ashwagandha while using thyroid hormone medications may cause additive effects.
Garlic Over 50% of prescription medications Moderate Garlic, when taken in amounts greater than what is typically found in food, might alter the function of cytochrome P450 (CYP) 3A4 and CYP2E1. The chemical “allicin” in garlic seems to be the cause of this interaction.
Glucosamine Warfarin (Coumadin) Major Taking glucosamine along with warfarin might increase INR and increase the risk of bleeding. This interaction has been reported in people taking glucosamine with or without chondroitin.
Green tea Hepatotoxic medications Moderate  Green tea extracts, but not the actual green tea beverage, have been linked to many reports of liver damage. There is concern that combining green tea extracts with hepatotoxic medications might have additive effects. 

Fruit Juices

Over 50% of prescription medications Moderate to Major Certain fruit juices can alter the absorption and/or metabolism of various medications. Depending on the juice, this can be due to the inhibition or induction of enzymes (including cytochrome P450, or CYP, enzymes) or transporters (such as organic anion-transporting polypeptides, or OATP).
Hypoglycemic Agents Medications for diabetes  Moderate to Major Using substances with hypoglycemic potential along with antidiabetes medications might have additive effects.
Red Yeast Rice HMG-CoA reductase inhibitors (“statins”) Moderate

Red yeast rice contains varying concentrations of the drug lovastatin. Combining red yeast rice with prescription statins might increase the chance of statin-related side effects including liver damage, muscle pain, and muscle damage.

Sedative Agents Medications with sedative effects Moderate to Major Some supplements can cause sedation and drowsiness. There is concern that combining these supplements with sedative medications might have additive effects. 

Serotonergic Agents

Medications with serotonergic effects

Moderate to Major Some supplements can increase serotonin levels. Combining these supplements with serotonergic medications can have additive effects, increasing the risk of serious side effects, including serotonin syndrome.
St. John’s wort Over 50% of prescription medications Moderate to Major St. John’s wort can induce various cytochrome P450 (CYP) enzymes, possibly reducing the effectiveness of many medications. 

*Not a comprehensive list. For comprehensive information, evidence, and ratings, go to our Interaction Checker.