Doctors in Singapore are on alert regarding herb-drug interactions following an incident last year, when a 58-year old woman died after surgical removal of a benign brain tumour.

The woman failed to inform doctors that she took cordyceps, a herbal medication, a week before her operation. This was believed to have led to extensive bleeding in her brain.

Patients need to understand that herbal medications are not completely safe, and that these preparations, when taken with other drugs, can alter 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 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.

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

1. Black Cohosh
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.

2. Coenzyme Q10
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.

3. Echinacea
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.

4. St. John's Wort supplements
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.

5. Ginseng
Ginseng is commonly used to improve the body’s resistance and vitality. There are four known types of ginseng, namely American, Korean, Siberian and Brazillian. 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.

6. Ginkgo biloba
Gingkgo 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. MIMS

Note: Article first published on 28 June 2016.