St John’s wort causes most drug interactions, finds review

BMJ 2012; 345 doi: (Published 29 October 2012) Cite this as: BMJ 2012;345:e7295
  1. Lilian Anekwe
  1. 1BMJ Evidence Centre

Warfarin, insulin, aspirin, digoxin, and ticlopidine had the greatest number of reported interactions with herbal and dietary supplements, a systematic review of 85 studies has found.

Most problems were caused by ingredients such as St John’s wort, magnesium, calcium, iron, and ginkgo, says the review in the International Journal of Clinical Practice.1 Each of these has been documented to interact with 147, 102, 75, 71, and 51 individual drugs respectively.

Researchers looked at 54 review articles and 31 original studies of people who took herbal medicines and dietary supplements at the same time as prescribed drugs, as well as books and websites, to find out more about the most common drug interactions and problems caused when herbal medicines and dietary supplements interfere with prescription drugs.

The literature covered 213 herbal and dietary supplement entities and 509 prescribed drugs, with 882 interactions described in terms of their mechanisms and severity.

More than 42% of the drug interactions were caused by the herbal and dietary supplement altering the pharmacokinetics of the prescribed drugs. Just over a quarter (26%) were described as major interactions.

Among the 152 identified contraindications, the most frequent involved the gastrointestinal system (16.4%), neurological system (14.5%), and renal/genitourinary diseases (12.5%).

Herbal and botanical remedies were more likely to have documented drug interactions and contraindications than the other dietary supplements, such as vitamins, minerals and amino acids, said one of the review authors, Hsiang-Wen Lin from the College of Pharmacy, China Medical School, Taiwan.

Flaxseed, echinacea, and yohimbe had the largest number of documented contraindications.

In an accompanying editorial Professor Edzard Ernst, emeritus professor at the University of Exeter, said that despite widespread use of “natural” remedies “our current knowledge is still woefully incomplete.”2

He believes that the number of interactions between herbal and dietary supplements and prescribed drugs could be under-reported and doctors can help quantify the problem.

“Patients deserve reliable information, and it is our duty to provide it,” writes Ernst. “We have to become vigilant and finally agree to monitor this sector adequately. Each individual doctor can contribute to this process by routinely including questions about alternative medicine use in their medical history taking.”


Cite this as: BMJ 2012;345:e7295


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