Metformin: What it does and how to use it safely

Metformin is the most commonly prescribed drug for type 2 diabetes. It lowers blood sugar without usually causing weight gain or frequent low blood sugar (hypoglycemia). People also use it for conditions like PCOS (polycystic ovary syndrome) because it can help with insulin resistance.

How metformin works and when it’s used

Metformin lowers glucose production by the liver and makes your body respond better to insulin. Doctors prescribe it first for most adults with type 2 diabetes. You might see it called immediate‑release (IR) or extended‑release (ER). IR is taken two to three times daily, ER is usually once daily and tends to cause fewer stomach issues.

Beyond diabetes, metformin is sometimes used off‑label for PCOS to help with irregular periods, ovulation, and insulin-related weight issues. Your doctor will decide if it fits your situation.

Common doses, timing, and simple tips

Typical starting doses are 500 mg once or twice daily or 850 mg once daily, then increased slowly to reduce stomach upset. Many people land on 1500–2000 mg per day split into doses with meals. Take metformin with food to cut nausea and diarrhea.

If you forget a dose, take it when you remember unless it’s almost time for the next one. Don’t double up to catch up.

Watch your kidneys: metformin is cleared by the kidneys, so doctors check your kidney function (eGFR) before starting and periodically after. It’s usually avoided or adjusted when eGFR is low. Tell your provider if you have heart failure, severe liver disease, heavy alcohol use, or upcoming imaging tests that require contrast dye—these can change how safe metformin is for you.

Common side effects are mild and mostly gastrointestinal: nausea, diarrhea, bloating. These often improve in a few weeks, especially with ER forms or gradual dose increases. A less common issue is vitamin B12 deficiency with long‑term use—your doctor may check B12 levels if you have numbness, fatigue, or anemia.

Lactic acidosis is a rare but serious risk. It’s most likely when kidney function is poor, after heavy alcohol use, or during severe dehydration or illness. Seek urgent care for unusual muscle pain, deep breathing, dizziness, or severe stomach upset.

Monitoring is simple: regular blood sugar checks, A1c tests every 3 months when changing therapy, and periodic kidney tests. If you plan to fast, have surgery, or get contrast imaging, ask your doctor whether to stop metformin temporarily.

Bottom line: metformin works well for many people, is inexpensive, and has a strong safety record when used with basic monitoring. Talk with your clinician about the right dose, check your kidneys and B12 when recommended, and stick to practical habits like taking it with food to reduce side effects.