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A common but relatively harmless side effect of metformin is a lingering metallic taste that won’t disappear. While it might be easy to think this is because the drug has somehow altered the taste receptors on our tongue, the actual reason is much more surprising.

In this research study by Nora Lee et al. (PMID: 25107910), they discovered that metformin accumulates in salivary glands due to a drug transporter, organic cation transporter 3 (OCT3). OCT3 acts like a selective pump, bringing metformin in from the blood and pushing it into the salivary gland. When saliva comes out in the mouth, we can thus taste metformin again, resulting in the metallic taste.

To alleviate this metallic taste, we thus recommend drinking more water or taking sugar free sweets. Most patients on metformin do report, however, that they get used to the medication over time and become less bothered by it. However, for patients who do feel their quality of life is impacted by metformin’s side effects, it is worthwhile talking to a doctor or pharmacist about it, as there are alternative medications that can be taken to control diabetes instead.