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Adverse reactions of natural health products/drugs under-reported, study shows

July 23, 2007

The adverse effects of using prescription drugs side by side with natural health products (NHP) are being under-reported, so the potential risks may be underestimated by health-care professionals and the public, a study from the University of Alberta in Edmonton, Canada shows.

A literature review and survey of 132 pharmacists revealed that while 47 per cent reported that they had encountered a patient with a suspected adverse event, only 1.5 per cent reported this to Health Canada. In contrast, 19 per cent of the pharmacists had reported adverse reactions to prescription or non-prescription drugs.

The study, co-authored by the U of A, the University of Toronto and Health Canada, is published in this month's issue of The Annals of Pharmacotherapy.

"The data show that adverse events are not being reported or are being under-reported at a dramatic rate," said Dr. Sunita Vohra, one of the study authors and an associate professor of pediatrics at the University of Alberta. "Natural health products should be treated with due respect." While the number of potential adverse events is low relative to the rates of NHP use in Canada, such products may be effective, but they may also have side effects, Vohra said. Natural health products include such products vitamins, minerals probiotics, St. John's wort, echinacea and garlic. There are 50,000 such products for sale in Canada.

In the survey, the majority of pharmacists felt they knew enough about just two drug-health product interactions to counsel patients. Adverse reactions can range from mild rashes and headaches to much more serious effects by patients using prescription medication such as blood thinners or insulin.

And while the pharmacists reported that they spent up to 30 minutes per day counselling patients on the use of natural health products, they estimated that only five per cent of patients who purchase products ask about potential drug interactions. "The public is less likely to see natural health products as risky," Vohra noted.

The lack of available data on interactions makes it difficult to provide patients and health care workers with useful advice for managing adverse reactions associated with these products. "To improve patient safety, new ways of capturing data are necessary," Vohra said. Possible ways to do that include active surveillance to monitor for harms. "Select pharmacies agree to be 'sentinel sites', actively asking every patient about possible adverse events, and reporting all data so we can learn which NHP-drug combinations are safe, and which aren't."

University of Alberta