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Diabetes Drug's Big Catch? A Fishy Odor

Metformin’s Dead Fish Smell May Cause Some to Discontinue Use
WebMD Health News
Reviewed by Louise Chang, MD

Feb. 16, 2010 -- The dead fish smell of a popular diabetes drug may cause some people to discontinue its use.

Metformin, an oral drug commonly used to treat type 2 diabetes, generally has few serious side effects, but gastrointestinal upset and nausea are common. Although these effects have been well documented in studies, researchers say one unique characteristic of the pills may have been overlooked as a potential cause of the nausea: their strong fishy odor.

Researchers say adverse reactions to the smell of metformin (sold generically and under the brand name Glucophage), have not been documented in medical literature, but hundreds of postings to message boards on the Internet note the strong fishy smell of the drug.

In their report, published in the Annals of Internal Medicine, researchers describe two cases in which patients discontinued use of generic metformin because of what they described as the nauseating smell of the drug.

Researchers say the odor, described as fishy or "like old locker room sweat socks," varies considerably between generic versions of metformin and seems to be more apparent with the immediate-release formulations.

"Our cases show that the distinctive odor of metformin (independent of other, well-known gastrointestinal adverse effects of the medication) causes patients to stop taking the drug," write researcher Allen L. Pelletier, MD, of the Medical College of Georgia in Augusta, and colleagues. "Patients may report that metformin nauseates them but do not further elaborate or distinguish this as a visceral reaction to the smell of the drug."

Instead, when patients stop taking metformin, researchers say physicians should ask about any reaction to the smell of the drug and try a film-coated, extended-release formulation of metformin as an alternative.

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