When you take metformin, a first-line oral medication for type 2 diabetes that helps lower blood sugar by reducing liver glucose production and improving insulin sensitivity. It's been used for over 60 years and is still the go-to drug for millions worldwide. But even though it’s widely prescribed, many people stop taking it because of side effects they weren’t prepared for.
One of the most common issues is gastrointestinal distress, including nausea, bloating, and diarrhea—especially when starting the drug or increasing the dose. Stomach upset isn’t rare; up to half of users experience it early on. But here’s the thing: most of the time, it gets better within a few weeks. Taking metformin with food, starting with a low dose, or switching to the extended-release version can cut these problems way down. It’s not a reason to quit—it’s a reason to adjust.
Another side effect people don’t talk about enough is vitamin B12 deficiency, a long-term risk that can lead to fatigue, nerve tingling, or even anemia if left unchecked. Low B12 happens because metformin interferes with how your gut absorbs it. Doctors don’t always check for it, so if you’ve been on metformin for more than a year and feel unusually tired or numb in your hands and feet, ask for a blood test. It’s simple to fix with supplements.
Then there’s the myth that metformin causes weight gain. Actually, it often does the opposite. Many people lose a few pounds on it—not because it’s a miracle fat burner, but because it reduces appetite and lowers insulin spikes that trigger hunger. That’s why it’s sometimes used off-label for PCOS or prediabetes, even in people who don’t have diabetes. But don’t expect dramatic results. The weight loss is modest, and it works best when paired with basic lifestyle changes.
What about the scary stuff? Lactic acidosis is rare—less than 1 in 30,000 users—but it’s serious. It happens when too much lactic acid builds up in your blood, usually when your kidneys aren’t working well or you’re dehydrated. That’s why you’re told to stop metformin before surgery or if you’re sick with vomiting or diarrhea. If you feel unusually weak, dizzy, or have trouble breathing, get help right away. But don’t panic. For most people, the risk is lower than the risk of uncontrolled diabetes.
Metformin isn’t perfect, but it’s one of the safest, cheapest, and most studied drugs out there. The side effects are usually mild, temporary, and manageable. The real danger isn’t the drug—it’s ignoring the signs or stopping without talking to your doctor. If your stomach feels off, don’t assume it’s just "normal." Ask for help. If you’re tired, don’t write it off as aging. Get your B12 checked. If you’re losing weight, that’s fine—but make sure it’s not from skipping meals because you’re afraid to eat.
Below, you’ll find real stories and practical advice from people who’ve been there: how they handled the nausea, why they switched forms, what worked for their B12 levels, and when they knew it was time to talk to their doctor. This isn’t just a list of side effects—it’s a guide to taking control without giving up on the medication that’s keeping you healthy.
