Pharmacists and patients are well aware that metformin may come with a fishy smell when you open the bottle. The smell does not mean the drug is spoiled, it's just due to it's inherent chemical characteristics.

Metformin (brand names: Glumetza, Riomet, Riomet ER) is associated with relatively few side effects, but nausea may be one of them, possibly due to this 'fishy' odor. Many patients may not be able to tolerate this medicine due to the odor.

According to a report published in the Annals of Internal Medicine, some extended-release, film-coated forms of metformin have a lower odor, and may be less likely to cause nausea. If you can't tolerate your metformin, let your doctor know. A switch to the extended-release form or a different manufacturer may do the trick.

Metformin is a widely prescribed medication for the initial treatment of type 2 diabetes, and may even be used in prediabetes. Don't stop treatment on your own, always consults with your doctor.

Related: Metformin side effects (in more detail)