Metformin is a widely used, first-line medication for type 2 diabetes that lowers blood sugar mainly by reducing the glucose the liver releases and helping the body respond better to insulin. It's taken by mouth and doesn't usually cause low blood sugar on its own.
Metformin is a medicine in the biguanide class and the usual first-line drug for type 2 diabetes. It lowers blood sugar mainly by reducing the amount of glucose the liver releases and by helping the body's cells respond better to its own insulin. On its own it doesn't usually cause low blood sugar (hypoglycemia), which is one reason it's so widely used.
What it's used for
Metformin is used alongside diet and exercise to manage type 2 diabetes. It's sometimes also used to help prevent diabetes in people with prediabetes, and to manage polycystic ovary syndrome (PCOS). Your clinician decides whether it's right for you based on your blood sugar, kidney function, and overall health.
How it's taken
Metformin is taken by mouth, usually with food to reduce stomach upset. Doctors typically start at a low dose and increase it gradually for the same reason, and an extended-release form is available that some people tolerate better. Always take it exactly as prescribed — follow your own prescription and the label rather than any general guidance, and don't change the dose without medical advice.
Common side effects
The most common side effects are digestive — nausea, diarrhea, stomach upset, and a metallic taste — and they often ease over time or when the dose is increased slowly and taken with food. Used long-term, metformin can lower vitamin B12 levels in some people, so this is sometimes checked. Tell your clinician if side effects are troublesome.
Warnings and interactions
Rarely, metformin can contribute to a serious condition called lactic acidosis, mostly in people with significant kidney problems, dehydration, serious infection, or heavy alcohol use. It's usually paused around procedures using contrast dye and some surgery. Tell your doctor about all your medicines and conditions, limit alcohol, and seek urgent care for symptoms like severe weakness, trouble breathing, unusual muscle pain, or feeling very unwell.
Who should talk to a doctor first
Discuss metformin with a clinician if you have kidney or liver disease, drink alcohol heavily, are pregnant or breastfeeding, or take other medicines. Never start or stop it on your own — managing type 2 diabetes safely means working with your healthcare team.
Pregnancy & breastfeeding
General information from the FDA-approved label and NIH's LactMed database — not a personal recommendation. Always discuss your own situation with a clinician.
In pregnancy
Sometimes used under clinician guidance (Only under specialist guidance)
Metformin is used in some pregnancies — for example, for gestational diabetes or PCOS — under a clinician's guidance.
While breastfeeding
Usually considered compatible (Usually considered compatible)
LactMed reports only small amounts in milk and no reported problems in breastfed infants.
Alcohol & food:Heavy alcohol use raises a rare risk of lactic acidosis with metformin — discuss safe limits with your clinician.
Sources: FDA label (DailyMed) · LactMed (NIH). The FDA replaced its old A/B/C/D/X pregnancy letter categories in 2015 with narrative label information.
Ways to save on Metformin
Prices vary by pharmacy, insurance, and location. These are general ways to lower the cost of most prescriptions — always confirm with your pharmacist.
Metformin is a low-cost generic, including extended-release versions. Cash prices are often very low; a 90-day supply usually saves the most.
Ask for the genericGeneric versions contain the same active ingredient at the same strength and usually cost far less than the brand. If a generic exists, ask your prescriber or pharmacist whether it's right for you.
Compare pharmaciesThe cash price for the exact same medicine can vary a lot between pharmacies — including large chains, supermarkets, warehouse clubs, and independents. It's worth calling a couple or checking a price-comparison service.
Cash price vs. insuranceSometimes a pharmacy's discounted cash price (or a coupon) beats your insurance copay. Ask the pharmacist to check both — you're allowed to pay whichever is lower.
90-day supplies & mail orderA 90-day fill, often through mail order, can cost less per month than three 30-day fills for stable, long-term medicines. Ask whether your plan offers it.
Manufacturer copay & savings cardsMany brand-name drugs have a manufacturer copay card or savings program that can lower the price for eligible, commercially-insured patients (these usually can't be used with government insurance like Medicare).
Patient assistance programsIf cost is a barrier, patient assistance programs (from the manufacturer, or nonprofits like NeedyMeds and RxAssist) may provide medicines free or at low cost based on income. A pharmacist or social worker can help you apply.
Don't ration or split to save — ask firstSkipping doses, stopping early, or splitting tablets to stretch a prescription can be unsafe. If the cost is hard, tell your clinician or pharmacist — there are almost always better options than going without.
We don't yet partner with a price-comparison service, so we show no prices here — the tips above apply to almost any prescription. If we add a disclosed pricing partner, it will appear here.
This is savings information, not medical advice. Never change how you take a medicine — skipping doses, stopping early, or splitting tablets — to save money without first asking your clinician or pharmacist.
Frequently asked questions
Metformin is mainly used, alongside diet and exercise, to manage type 2 diabetes by lowering blood sugar. It's the usual first-line medicine for the condition. It's also sometimes used for prediabetes prevention and to help manage polycystic ovary syndrome (PCOS).
It lowers blood sugar primarily by reducing the amount of glucose the liver releases into the blood, and by helping the body's cells respond better to insulin. Unlike some diabetes medicines, it doesn't usually cause low blood sugar on its own.
The most common are digestive — nausea, diarrhea, stomach upset, and a metallic taste — which often ease over time, especially when the dose is increased slowly and taken with food. Long-term use can lower vitamin B12 in some people. Serious side effects are rare.
On its own, metformin doesn't usually cause low blood sugar (hypoglycemia), which is one of its advantages. However, low blood sugar can happen when it's combined with other diabetes medicines such as insulin or sulfonylureas, or with heavy alcohol use.
Don't stop metformin without talking to your clinician — stopping can let your blood sugar rise. Some people whose type 2 diabetes improves a lot through weight loss and lifestyle changes may be able to reduce or stop it under medical supervision, but that's a decision to make with your healthcare team.