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What is Metformin?
Metformin is a prescription medicine used to help manage blood sugar in adults and children with type 2 diabetes. It is also used in some cases of insulin resistance, prediabetes, and polycystic ovary syndrome when prescribed off label. Metformin belongs to a class of medicines called biguanides and is considered the first line choice for most people with newly diagnosed type 2 diabetes. It is available as immediate release tablets in 500 mg, 750 mg, 850 mg, and 1000 mg strengths, and as extended release tablets in 500 mg and 750 mg strengths for once daily dosing.
Metformin can be used alone or with other diabetes medicines, including insulin. Many people take it long term to maintain stable blood sugar and protect against diabetes related complications. Because it is widely available as a generic, some patients compare pharmacies for cheap refills or buy metformin online from licensed U.S. pharmacies to lower monthly costs. Always confirm the source is legitimate and the label matches your prescription.
How It Works
Metformin lowers blood sugar primarily by reducing glucose production in the liver, improving the body's sensitivity to insulin, and enhancing glucose uptake by muscle cells. Unlike some diabetes medicines, it does not cause the pancreas to release more insulin, which makes it less likely to cause low blood sugar when used alone.
Metformin also has modest effects on gut microbiota and may slightly reduce intestinal glucose absorption. These combined actions help smooth blood sugar levels throughout the day. Some research suggests cardiovascular benefits and possible weight stabilization, which adds to its appeal in long term diabetes care.
What you may notice
Lower fasting blood sugar and steadier after meal readings, modest weight loss or stability, and sometimes improved energy. Gastrointestinal side effects like mild diarrhea or stomach upset may appear at first but usually improve with food and slow dose increases.
Dosage Information
Dosing is individualized. The goal is to reach an effective dose without causing intolerable stomach upset. Always follow your prescription and do not stop or change your dose without guidance.
- Immediate release start: 500 mg once or twice daily with meals, or 850 mg once daily. Increase by 500 mg weekly or 850 mg every 2 weeks as tolerated.
- Usual effective dose: 1500 mg to 2000 mg daily in divided doses. Maximum is generally 2550 mg daily in adults.
- Extended release start: 500 mg once daily with the evening meal. Increase by 500 mg weekly as tolerated, up to 2000 mg once daily in most cases.
How to take it
Take with food to reduce stomach upset. Swallow tablets whole; do not crush or chew. For extended release, take at the same meal each day. If you miss a dose, take it when remembered unless it is close to the next one—then skip the missed dose. Do not double up.
Cost and access tips
Generic metformin is inexpensive and widely available. Buying refills online from licensed pharmacies can reduce cost. Cheap pricing is fine when the label, strength, and expiration date are clear, and a pharmacist is available for questions.
Side Effects
Common side effects include diarrhea, nausea, stomach discomfort, gas, and a metallic taste. These are more common at the start and usually improve over time. Starting with a low dose and increasing slowly helps minimize discomfort.
Less common but important
- Lactic acidosis: A rare but serious condition that can occur if metformin builds up in the blood, usually in people with severe kidney problems, severe infection, dehydration, or heavy alcohol use. Symptoms include muscle pain, weakness, trouble breathing, unusual fatigue, stomach pain, dizziness, or irregular heartbeat. Seek emergency care immediately if suspected.
- Vitamin B12 deficiency: Long term use can lower B12 levels, leading to anemia or nerve problems. Periodic B12 checks are recommended.
Tell your clinician if side effects persist or worsen. Never stop metformin suddenly without medical advice if you are using it to control blood sugar.
Warnings & Interactions
Metformin should not be used in people with severe kidney disease, unstable heart failure, or severe liver problems. Use caution with dehydration, major surgery, or serious illness, as these can increase the risk of lactic acidosis.
Drug interactions
- Contrast dye for imaging tests: Can increase the risk of lactic acidosis. Metformin is usually paused before and after these procedures.
- Alcohol: Heavy drinking increases lactic acidosis risk. If you drink, keep it moderate and consistent.
- Certain heart or blood pressure medicines: Diuretics, ACE inhibitors, and beta blockers may affect blood sugar or kidney function; monitoring is important.
Practical safety tips
Check kidney function before starting and at least yearly. Monitor blood sugar regularly. Carry a medical alert card stating you have diabetes and take metformin. If buying online, choose licensed U.S. pharmacies with clear labeling and expiration dates. Cheap pricing is fine when those checks are met.
Frequently Asked Questions
Blood sugar improvements can be seen within a few days, but full benefits for fasting and post meal glucose may take up to 2 weeks of regular use.
Not usually when taken alone, because it does not stimulate insulin release. Low blood sugar is more likely if combined with insulin or certain other diabetes medicines.
Some people experience modest weight loss or stability on metformin, especially if combined with healthy eating and physical activity.
Take it when remembered unless it is almost time for the next dose. If so, skip the missed dose. Do not double up.
Light drinking may be tolerated, but heavy or binge drinking increases the risk of lactic acidosis and should be avoided.
Yes, it is often paused before major surgery or procedures using contrast dye, then restarted when kidney function is confirmed as stable.
No, diarrhea and stomach upset are common early side effects that usually improve within a few weeks. Taking it with food and using extended release forms can help.
It is safe for many people with mild kidney impairment but not for severe kidney disease. Your clinician will check kidney function before starting and regularly afterward.
Yes, if you use a licensed U.S. pharmacy with clear labeling and expiration dates. Cheap pricing is fine when those checks are met.
Yes, it can be combined with many other diabetes medicines, but the risk of low blood sugar increases with insulin or sulfonylureas, so monitoring is important.
Medical Disclaimer
This website provides informational overviews of medications and does not offer medical advice, diagnosis, or treatment. Always consult a licensed healthcare provider before starting or changing any medication.
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This page was last medically reviewed: August 2025
Educational information only. Metformin should be used under clinician supervision with periodic kidney function checks and blood sugar monitoring. Not for people with severe kidney impairment.