Metformin: What It Does and How to Use It Safely

Metformin is one of the most prescribed medicines for type 2 diabetes. It lowers blood sugar without usually causing low blood sugar on its own. People also use it for prediabetes and polycystic ovary syndrome (PCOS). If you want a clear, practical guide—how to take it, what to watch for, and how to stay safe—keep reading.

How metformin works and who should take it

Metformin belongs to a class called biguanides. It reduces glucose production by the liver and helps your body use insulin better. Doctors often start it when lifestyle changes alone don’t control blood sugar. It’s a good first choice for many because it’s affordable, well-studied, and can help with modest weight loss or weight neutrality.

Not everyone should take metformin. If you have severe kidney problems, serious liver disease, or conditions that can cause low oxygen (like severe heart or lung disease), your doctor may avoid it. Always tell your prescriber about any other conditions, alcohol use, or recent infections—these matter for safety.

Practical tips: dosing, side effects, and safety checks

Start low and go slow. A common start is 500 mg once daily with a meal, then increase after a week or two. Many people take 500 mg twice daily or switch to an extended-release version once daily. Typical daily doses range up to about 2,000–2,500 mg, but your doctor will set the right maximum for you.

Expect stomach issues early on: nausea, gas, or loose stools are common. Taking metformin with food and splitting doses helps. If GI side effects don’t ease after a few weeks, talk to your doctor—switching to extended-release often helps.

Watch for rare but serious risks. Lactic acidosis is very uncommon but serious—symptoms include unusual tiredness, muscle pain, trouble breathing, or feeling cold. If you have these, seek immediate care. Also, metformin can lower vitamin B12 over time, so ask about a B12 check if you feel numbness, tingling, or unusual fatigue.

Before any imaging test that uses iodinated contrast dye, mention metformin. Your provider may tell you to stop it briefly depending on kidney function. Speaking of kidneys: your doctor should check your kidney function (eGFR) before starting metformin and periodically after that.

Combine with lifestyle, not instead of it. Diet changes, weight management, and exercise are still central. If you’re on insulin or sulfonylureas too, be aware the risk of low blood sugar increases—learn symptoms and how to treat hypoglycemia.

If you have questions about taking metformin with other meds, pregnancy, or breastfeeding, ask your clinician. Small adjustments make a big difference in comfort and safety—so get a plan that fits your life.