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

When you’re prescribed metformin, a first-line medication for type 2 diabetes that lowers blood sugar by reducing liver glucose production and improving insulin sensitivity. Also known as Glucophage, it’s one of the most common pills for diabetes worldwide. But knowing how it works isn’t enough—you need to know what it can do to your body. While many people take metformin without issues, side effects are real, common, and often avoidable if you understand them early.

Most people experience mild gastrointestinal upset, digestive problems like nausea, diarrhea, or stomach cramps that usually fade after a few weeks. These aren’t signs the drug isn’t working—they’re just your gut adjusting. Taking metformin with food, starting with a low dose, or switching to the extended-release version can cut these symptoms in half. Less common but more serious are vitamin B12 deficiency, a slow, silent drop in B12 levels that can cause fatigue, nerve tingling, or brain fog over time. If you’ve been on metformin for more than a year, ask your doctor to check your B12. It’s a simple blood test, and fixing it is easy with supplements.

Some people worry about lactic acidosis, a rare but dangerous buildup of lactic acid in the blood. It’s extremely uncommon—less than 1 in 10,000 users—and mostly happens if you have kidney problems, severe dehydration, or drink alcohol heavily. If you’re healthy and follow your doctor’s advice, your risk is near zero. But if you feel unusually tired, dizzy, or have trouble breathing, get help right away.

Metformin isn’t for everyone. If you have advanced kidney disease, severe heart failure, or are getting certain types of contrast dye for imaging tests, your doctor will pause or avoid it. But for most people with type 2 diabetes, it’s the safest, cheapest, and most effective starting point. It doesn’t cause weight gain like some other diabetes drugs, and studies show it may even lower heart disease risk. That’s why it’s still the go-to choice after 60 years on the market.

Still, you’re not stuck with it. If side effects stick around or you need more help controlling your blood sugar, there are other options—like SGLT2 inhibitors, medications that make your kidneys flush out extra sugar, or GLP-1 agonists, injections that slow digestion and help you lose weight. These newer drugs can work alongside metformin or replace it if needed.

What you’ll find below isn’t just a list of articles—it’s a practical guide to real-world issues with metformin. From how to handle nausea without quitting the pill, to why some people stop taking it and what they switch to, to how it compares with other diabetes meds. You’ll see what works, what doesn’t, and what most patients wish they’d known before starting.