Health Updates

Drug Interactions with Herbal Medicines You Need to Know

The possibility of drug interactions, direct toxicities, and contamination with active pharmaceutical agents are among the safety concerns about dietary and herbal supplements.


Photo: Herbal Supplements | InStyleHealth

Although there is a widespread public perception that herbs and botanical products in dietary supplements are safe, research has demonstrated that these products carry the same dangers as other pharmacologically active compounds.


Interactions may occur between prescription drugs, over-the-counter drugs, dietary supplements, and even small molecules in food—making it a daunting challenge to identify all interactions that are of clinical concern.


Concerns about herb-drug interactions are often not based on thorough research. Most herb-drug interactions classified in current sources are hypothetical, inferred from animal studies, cellular assays, or based on other indirect means; however, attention to this issue is needed for drugs with a narrow therapeutic index, such as cancer chemotherapeutic agents, warfarin, and digoxin.


However, many other supplements are predicted to cause interactions based only on in vitro studies that have not been confirmed or have been refuted in human clinical trials.


Some supplements may cause interactions with a few medications but are likely to be safe with other medications. Some supplements have a low likelihood of drug interactions and, with certain caveats, can safely be taken with most medications.


Below are some of the most common herbs used as supplements, together with some of their known interactions with drugs:


Black cohosh – is often used for menopausal disorders. It could be toxic to the liver and could have an increased toxic effect to liver when used together with other drugs that can also cause liver toxicity. Drugs that depend on the liver for their excretion may accumulate and lead to toxicity when used with black cohosh.


Coenzyme Q10 – protects the heart from damage from cancer medications. The use of coenzyme Q10 with warfarin decreases its blood thinning effects and may increase the risk for a blood clot.


Echinacea – is used to enhance the body’s immune system and helps in the management of the common cold. Echinacea affects the metabolism of drugs by the CYP450 system. This could lead to complicated drug interactions, enhancement of side effects and reduction of the drug’s therapeutic effects. It can also slow down the metabolism of caffeine which can lead to insomnia, jitteriness and headache.


Gingko biloba – is used to enhance memory, and in improving symptoms of Alzheimer’s and Parkinson’s diseases. It can decrease effects of certain HIV medications, and alter the actions of drugs metabolized by the liver.


Ginseng – is commonly used to improve the body’s resistance and vitality. There are four known types of ginseng, namely American, Korean, Siberian and Brazilian. Of these, American ginseng is known to decrease the effects of warfarin and should not be used together with other anticoagulants, though this cannot be conclusively said for the other three types. Ginseng also has an effect in blood pressure and blood sugar medications.


St. John’s Wort – Supplements containing St. John’s Wort are commonly used to treat symptoms of depression. This should not be used concomitantly with other antidepressants, migraine medications, dextromethorphan, warfarin, birth control pills, and certain antiretroviral medications due to seriousness of drug interactions.


Herbs are coming under increasing attack for being potentially dangerous to patients who are already taking prescription medications. The concerns are multiplied for those patients currently taking multiple medications, often prescribed by multiple physicians who may or may not be in communication with each other regarding their medical reasoning.


Patients need to realize that herbal medications are not completely safe, and that these preparations, when taken with other drugs, can change the way that the drug is processed and excreted by the body, enhance a drug’s side effects, or block the intended therapeutic effect of the drug.


It is important that patients must consult first with a physician before taking any herbal supplements, or inform their physician if they are taking herbal preparations if they are prescribed with medications.

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