Metformin Side Effects: What You Need to Know Before Taking It

When you’re diagnosed with type 2 diabetes, your doctor likely prescribes metformin, a first-line oral medication used to lower blood sugar by improving insulin sensitivity and reducing liver glucose production. Also known as Glucophage, it’s been the go-to drug for decades because it’s cheap, effective, and doesn’t cause weight gain or low blood sugar like other options. But even the safest drugs have trade-offs—and metformin is no exception. Thousands of people take it daily without issue, but others experience side effects that can be uncomfortable, confusing, or even dangerous if ignored.

One of the most common issues is gastrointestinal distress, stomach cramps, nausea, diarrhea, and gas that often appear in the first few weeks of use. These aren’t rare—they happen in up to half of new users. Most improve over time, but if they don’t, your doctor might lower your dose or switch you to an extended-release version. It’s not a sign you’re allergic—it’s your gut adjusting. Then there’s the less-known but serious risk: vitamin B12 deficiency, a slow, silent side effect that can cause nerve damage, fatigue, and brain fog over years of use. Studies show up to 30% of long-term metformin users develop low B12 levels. That’s why checking your B12 every year is just as important as checking your blood sugar.

Metformin also interacts with other drugs and conditions. If you have kidney problems, especially if your eGFR drops below 30, your doctor should pause or adjust your dose. It’s not because metformin damages kidneys—it’s because your kidneys can’t clear it properly, raising the risk of lactic acidosis, a rare but life-threatening buildup of acid in the blood. That’s why labs matter. And if you’re scheduled for surgery or a CT scan with contrast dye, you’ll need to stop metformin temporarily. These aren’t warnings to scare you—they’re safeguards built into the drug’s safety profile.

What you won’t hear from every doctor: metformin isn’t just for diabetes. It’s used off-label for PCOS, prediabetes, and even weight management in some cases. But that doesn’t mean it’s harmless for everyone. If you’re not diabetic, your body doesn’t need the same level of glucose control—and side effects might outweigh benefits. Always ask: Why am I taking this? What am I trying to fix? The answer changes how you monitor your health.

Below, you’ll find real stories and practical advice from people who’ve lived with metformin side effects. Some found ways to reduce nausea without quitting. Others caught B12 deficiency before it damaged their nerves. A few learned when to speak up when their doctor dismissed their symptoms. These aren’t just articles—they’re survival guides for anyone on this drug.