What does metformin do to your mouth?

October 10, 2025 •

2 min read

Metformin is a first-line treatment for Type 2 diabetes used by over 120 million people worldwide. While primarily known for its role in blood sugar control, patients often wonder, "What does metformin do to your mouth?" The drug is known to cause a metallic taste, but emerging research also points to potential benefits for oral health.

Quick Summary

Metformin's effects on the mouth include a common side effect of metallic taste, as the drug is secreted into saliva. It can also cause dry mouth and, over the long term, may lead to vitamin B12 deficiency and tongue inflammation. Conversely, studies suggest metformin could offer protective benefits against gum disease by reducing inflammation and promoting bone health.

Key Points

Metallic Taste: A metallic or bitter taste is a common side effect of metformin, particularly when starting treatment, because the drug is excreted into the saliva.
Dry Mouth Risk: Dry mouth (xerostomia) is also a potential side effect for some users, which can be linked to other issues like dehydration.
B12 Deficiency: Long-term metformin use can cause a vitamin B12 deficiency, which may lead to glossitis, an inflammation that causes a smooth, sore, red tongue.
Gum Disease Benefits: Emerging research suggests metformin can have positive effects on periodontal disease by reducing inflammation and preventing bone loss in the jaw.
Management Strategies: Management involves taking the medication with meals, staying hydrated, using sugar-free gum, and monitoring B12 levels with a doctor.
Connection with Diabetes: The effects of metformin are closely linked to the overall impact of diabetes on oral health, including increased risk of gum disease and oral infections.

The Common Complaint: Metallic Taste (Dysgeusia)

One of the most frequently reported oral side effects of starting metformin is a metallic taste, medically known as dysgeusia. This occurs because the medication is excreted into the saliva, a process involving the organic cation transporter-3 (OCT3) in the salivary glands. For many, this taste is temporary, resolving within a few weeks as the body adjusts, but it can be persistent for some. Discussing persistent taste disturbances with a healthcare provider may lead to relief through dose adjustment or switching to an extended-release form.

Potential for Dry Mouth (Xerostomia)

While less common than a metallic taste, some individuals report dry mouth while taking metformin. This can sometimes be an indirect effect of other side effects like dehydration from diarrhea. Chronic dry mouth increases the risk of cavities, gum disease, and oral infections. Staying well-hydrated is a key management strategy.

The Vitamin B12 Connection: Glossitis and Tongue Issues

Long-term metformin use can reduce vitamin B12 absorption, potentially leading to a deficiency. One symptom of a B12 deficiency is glossitis, or inflammation of the tongue. This can result in a smooth, red, and sometimes sore or burning tongue. If these symptoms occur, consult a healthcare provider to check B12 levels; supplementation may be needed.

A Surprising Twist: Potential Benefits for Gum Disease

Recent research indicates metformin may offer benefits for periodontal disease (gum disease). Studies suggest metformin can help manage inflammation, prevent jaw bone loss, and inhibit osteoclast activity. It may also have direct antibacterial effects against pathogens in the mouth. This is particularly relevant given the link between diabetes and gum disease. Metformin's ability to manage both inflammation and glucose could improve oral health outcomes.

Oral Health Effects of Metformin: A Comparison


Side Effect	Description	Cause	Management
Metallic Taste (Dysgeusia)	An unpleasant, persistent metallic taste, especially when starting the medication.	Excretion of the drug into saliva via the OCT3 transporter.	Often temporary. Taking with food, staying hydrated, using plastic utensils.
Dry Mouth (Xerostomia)	Reduced saliva production leading to a dry sensation.	Less common direct effect, potentially linked to dehydration caused by GI upset.	Stay hydrated, use sugar-free gum, limit caffeine/alcohol, consider extended-release version.
Glossitis	A smooth, red, and sore or burning tongue.	Long-term metformin use can inhibit vitamin B12 absorption.	Consult a doctor for B12 level checks; may require B12 supplementation.
Potential Benefit	Description	Mechanism	Relevance
Periodontal Health	Improved gum health, reduced inflammation, and potential prevention of bone loss.	Reduces systemic inflammation, modulates sugar metabolism, inhibits bone-resorbing cells (osteoclasts).	Offers a systemic approach to mitigating gum disease, a common complication of diabetes.

Conclusion

Metformin impacts oral health with both potential side effects and emerging benefits. Consult a healthcare provider for persistent symptoms or B12 concerns.

Frequently Asked Questions

Metformin causes a metallic taste, known as dysgeusia, because the drug is excreted into the saliva. Studies have shown this process is mediated by the organic cation transporter-3 (OCT3), causing the medication to accumulate in the salivary glands.

For most people, the metallic taste from metformin is temporary and subsides within the first few weeks as the body adjusts to the medication. If the issue persists, a healthcare provider may suggest strategies like taking the medication with food or switching to an extended-release version.

Yes, long-term metformin use can inhibit the absorption of vitamin B12, potentially leading to a deficiency. A symptom of this deficiency is glossitis, an inflammation of the tongue that can cause it to become sore, smooth, and red.

Recent studies suggest that metformin can be beneficial for periodontal disease. By reducing systemic inflammation and inhibiting the bone-resorbing activity of osteoclasts, it may help to prevent bone loss in the jaw and improve gum health.

While not a universally reported side effect, some individuals do experience dry mouth (xerostomia) when taking metformin. It is sometimes linked to other side effects like dehydration caused by diarrhea.

To manage a metallic taste, try taking your metformin with food to reduce GI upset. Staying well-hydrated by drinking plenty of water and chewing sugar-free gum can also help stimulate saliva flow and mask the taste.

Unmanaged diabetes itself can cause taste changes due to high blood sugar damaging nerves. In the case of metformin, the metallic taste is a direct side effect of the drug being secreted into saliva, separate from the effects of the underlying diabetes.