Mixing herbal medicines and prescriptions could pose undiscovered health risks because many negative reactions aren't being reported or tracked, a new study suggests.

The adverse effects of taking prescription drugs with natural health products are dramatically under-reported or not reported at all, so their potential risks may be underestimated by health-care professionals and the public, the study found.

"People look at risks based on what's known. If it's not being reported, it can't be known," said Dr. Sunita Vohra, an associate professor of pediatrics at the University of Alberta and the study's lead author.

'Treat products with respect — if they can help you, they can potentially harm you." —Dr. Sunita Vohra, University of Alberta

The study found almost half the 132 pharmacists surveyed had seen a potential adverse reaction in patients who mixed prescription drugs and natural products, but only two of them reported the incidents to Health Canada.

By contrast, 19 per cent of pharmacists said they had reported adverse events from mixing prescription and non-prescription drugs.

The finding startled the study's co-authors — researchers from University of Alberta, the University of Toronto and Health Canada.

"We didn't anticipate the number of potential natural health product-drug interactions that community pharmacists were seeing, nor did we anticipate their reporting levels," said Vohra.

Researchers suggest the health-care system needs a better method of tracking the incidents encountered by consumers using both prescription and herbal medicines.
(CBC)

Adverse events ranged from mild rashes and headaches to more serious consequences for some patients. Those on prescribed blood thinners, for example, can put their health at risk if they take natural products that they may not realize also act as blood thinners.

Researchers call for better tracking system

Vohra said a large proportion of the Canadians who use natural products also use prescription medication, and the health-care system needs a better method of tracking the incidents encountered by consumers using both products.

"We're not saying natural health products aren't safe," said Vohra. "We're not saying they are safe, or that you can't ever use them with drugs, or that you must use them with drugs. There's no way we have enough information to make those sorts of absolute statements."

Consumers need to handle natural health products with caution, Vohra said.

"Treat products with respect — if they can help you, they can potentially harm you," Vohra said.

Heather Boon, a University of Toronto pharmacy professor, said she finds it troubling that pharmacists aren't reporting adverse events, although she knows from personal experience that they are busy and often don't have time for added paperwork.

Boon said a followup study is underway looking at the under-reporting. Vohra noted consumers can also file reports on adverse reactions to Health Canada.