Metformin can come with a significant downside: a distinct, fishy smell that, for some people, is enough to cause them to stop taking it. 

Metformin pills spilling out of a bottle onto a table

Key facts

  • A distinct, unpleasant, fishy odor can prevent some people from taking their prescribed metformin.
  • Although not commonly discussed in the medical literature, experts are aware of the issue and recommend several simple strategies if your metformin smells bad.

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Issues with metformin’s fishy odor are not often discussed

Despite being the most widely prescribed diabetes medicine, this issue isn’t widely reported in medical literature. However, it is frequently discussed in online forums and among pharmacists, who can often recognize the drug by its odor alone.

Historical accounts, including a 2010 report published in the Annals of Internal Medicine, highlight this concern. In this paper, two adult men with type 2 diabetes reported a “dead fish” smell so off-putting that it led them to stop taking the medication. 

This study brought to light that while not commonly reported, the scent could indeed influence how willing people are to take the medicine and could even be a cause behind certain common metformin side effects such as nausea.

Why does my metformin smell bad?

Dr. May noted that this smell might raise concerns about the medicine’s quality, stating that

“Metformin is an excellent drug, but the immediate-release formulation may have an odor to it. The smell is fishy or like the inside of an inner tube, and in a patient’s mind…they may think the drug isn’t good.”

However, according to manufacturers, no link has been established between the medicine’s odor and its effectiveness — the scent is simply a characteristic of the drug.

People who are considering discontinuing metformin due to its odor are strongly advised to speak with their healthcare providers. Exploring alternative formulations or strategies could provide a better solution without compromising diabetes management.

Ways to deal with metformin’s bad smell

Experts have suggested several strategies to overcome the odor-related challenges with metformin. 

One effective solution for those affected is switching to a film-coated, extended-release (ER or XR) version of the drug, which typically has a much less noticeable smell.

Additionally, a simple but practical tip suggested by report co-author J. Russell May, PharmD, FASHP, for those sensitive to the smell is to hold their nose while taking the medication.

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