Metformin is one of the most commonly prescribed drugs for type 2 diabetes. It’s generally safe and well-studied—but some side effects can catch people off guard, especially early on.
Here are 10 side effects that many patients don’t expect:
1. Metallic taste in the mouth
A strange, bitter or metallic taste is surprisingly common when starting metformin.
2. Loss of appetite
Some people feel less hungry, which can lead to mild weight loss.
3. Unintended weight loss
Often considered a benefit, but it can be unexpected if you’re not trying to lose weight.
4. Vitamin B12 deficiency (long-term)
Over time, metformin can reduce B12 absorption, which may lead to fatigue, numbness, or tingling.
5. Diarrhea
One of the most common side effects—especially when first starting or increasing the dose.
6. Gas and bloating
Digestive discomfort can occur as your body adjusts.
7. Nausea
Usually mild and temporary, often improved by taking the medication with food.
8. Cold sensitivity or feeling chilled
Some people report feeling unusually cold, though it’s not widely discussed.
9. Skin reactions
Rashes or itching can happen, but they’re uncommon.
10. Rare but serious: lactic acidosis
A very rare condition where lactic acid builds up in the blood. Symptoms may include:
- Extreme fatigue
- Muscle pain
- Trouble breathing
This is uncommon but serious, and needs immediate medical attention.
What’s actually common vs uncommon?
- Common: diarrhea, nausea, bloating
- Less common: metallic taste, appetite changes
- Rare: B12 deficiency (long-term), skin reactions, lactic acidosis
Practical tips
- Take metformin with meals to reduce stomach issues
- Ask about extended-release (XR) versions if side effects persist
- Consider periodic B12 checks if you use it long-term
If you want, I can compare metformin vs other diabetes medications or help you figure out whether a symptom you’re noticing is likely related.
