Herbal Drugs - Reactions with Other Drugs or Substances

Reactions with Other Drugs or Substances

"Herbs have the reputation of being natural and gentle," explained registered dietician Karen Collins on MSNBC.com, "but they contain compounds that can profoundly affect the body." Self-medicating with herbal drugs can be risky, especially among patients who take prescription drugs.

The Truth about Guarana

The stimulant guarana (gwah-rah-NAH) is sold as an herbal tonic that supposedly increases endurance. Actually, it is just a natural form of caffeine. (An entry on caffeine is available in this encyclopedia.) Guarana is made from the mashed seeds of the Paullinia cupana, a woody Brazilian shrub. The per-tablet dosage provides the user with about as much caffeine as a cup of coffee. Guarana is an active ingredient in many caffeinated energy drinks.

Most herbals have not yet been studied for possible interactions with prescription drugs, but some information is already available. For example, valerian may intensify the sedative effects of

Various forms of St. Johns wort are displayed. The dried buds and flowers of this plant are used to treat depression and anxiety. DK Limited/Corbis.
Various forms of St. John's wort are displayed. The dried buds and flowers of this plant are used to treat depression and anxiety. © DK Limited/Corbis.

barbituratesPronounced bar-BIH-chuh-rits; drugs that act as depressants and are used as sedatives or sleeping pills; also referred to as 'downers.', so they should not be taken together. (A separate entry on barbiturates is available in this encyclopedia.)

According to an NIH study, garlic supplements can slow the time it takes for blood to clot. Because of garlic's blood-thinning properties, it should be used with caution by patients who are already on blood-thinning drugs. High-dosage garlic supplements are also thought to decrease the effectiveness of certain drugs used to fight AIDS (acquired immunodeficiency syndrome).

The American Botanical Council noted that St. John's wort interacts with a variety of prescription drugs, "lowering their levels and effectiveness." According to a National Institute of Mental Health (NIMH) publication on depression, patients being treated with FDA-approved prescription medications for AIDS, heart disease, depression, seizures, certain cancers, and transplant rejection should not take St. John's wort.