Metformin is a prescription medicine for type 2 diabetes. This page explains how it works, how to take it safely, what to expect, how much it may cost in the USA, how the law regulates it, and what alternatives exist. Use the quick links below to jump to a section.

At a glance

Active ingredient: metformin

Primary condition: type 2 diabetes mellitus

Common strengths in the USA: 500 mg and 850 mg tablets (immediate-release). Other strengths may include 1000 mg IR and 500 mg or 750 mg extended-release (ER), depending on the manufacturer.

What Metformin is used for

Metformin helps control blood sugar in adults and children with type 2 diabetes. It is used along with diet, physical activity, and weight management. It can be prescribed alone or combined with other anti-diabetic drugs, including insulin. For guidance on who should not take it, see Warnings and precautions.

How to take Metformin

Always follow your prescriber’s directions. General tips:

  • Take Metformin with food to reduce stomach upset.
  • Try to take it at the same times each day for steady control.
  • Keep taking it even if you feel well, unless your clinician tells you to stop.
  • Ask your healthcare provider if you have questions about timing, meals, or interactions.

Monitoring typically includes blood glucose checks and regular A1c testing. Your clinician may also monitor kidney function before and during treatment.

How it works (drug class and mechanism)

Metformin belongs to a class called biguanides. It lowers glucose mainly by:

  • Reducing the amount of sugar your liver makes.
  • Decreasing sugar absorption from the intestines.
  • Improving the body’s sensitivity to insulin.

If you miss a dose

If you forget a dose and it has not been long, take it when you remember. If it is almost time for your next dose, skip the missed dose. Do not take two doses at once.

Storage

Store at 68 to 77 F (20 to 25 C). Short periods at 59 to 86 F (15 to 30 C) are acceptable. Keep away from moisture, heat, and light. Do not store in the bathroom. Keep out of reach of children and pets.

Warnings and precautions

Do not use Metformin if any of the following apply to you:

  • You have severe kidney problems or cannot clear contrast dye properly, or you are scheduled for certain imaging studies with iodinated contrast without prescriber guidance to hold and restart the medicine.
  • You are allergic to metformin or any tablet ingredient.
  • You have severe dehydration, a serious infection, or low blood oxygen levels.
  • You have metabolic acidosis, including diabetic ketoacidosis.
  • You have advanced liver disease.
  • You recently had a heart attack, have shock, or unstable heart failure requiring treatment.
  • You are age 80 or older and have not had a recent kidney function test.
  • You have a history of stroke with unstable clinical status.

Important safety notes

  • Metformin by itself usually does not cause low blood sugar. The risk of hypoglycemia rises if you skip meals, drink alcohol, exercise heavily, or take other diabetes medicines such as insulin or sulfonylureas at the same time. Keep a quick source of sugar nearby (glucose tablets/gel, juice, or regular soda).
  • Gastrointestinal upset (nausea, stomach discomfort, diarrhea) is common early on and often improves. If severe or new stomach symptoms occur later, contact your clinician to rule out lactic acidosis.
  • Lactic acidosis is rare but serious. Risk factors include kidney impairment, dehydration, heavy alcohol use, severe infection, or poor tissue oxygenation. Seek medical care urgently for unusual muscle pain, feeling very weak, shortness of breath, or persistent abdominal pain.
  • Limit alcohol. Discuss any alcohol use with your prescriber.
  • Tell your dentist, surgeon, or any emergency provider that you take metformin. Your prescriber may advise holding metformin around surgery or certain tests and restarting after kidney function is confirmed.
  • Follow your individualized diet and exercise plan consistently.
  • Elderly patients may be more sensitive to side effects, and signs of low blood sugar may be harder to recognize.
  • Not generally recommended in children under 10 years old unless directed by a specialist.
  • If you become pregnant, contact your clinician to discuss treatment options. Ask your clinician before breastfeeding.

For side effects, see Possible side effects. For access rules in the USA, visit Legal and access in the USA.

Possible side effects

Common, often temporary

  • Diarrhea
  • Upset stomach or indigestion
  • Nausea or vomiting
  • Gas
  • Headache
  • Metallic taste

Serious - get medical help right away

  • Signs of lactic acidosis: unusual muscle pain or weakness, deep or fast breathing, feeling unusually cold, severe tiredness, slow or irregular heartbeat, persistent abdominal pain
  • Severe allergic reactions: rash, hives, itching, swelling of face, lips, tongue, or throat, trouble breathing
  • Chest pain, dizziness, fainting, fever or chills with sore throat, or a general feeling of being very unwell

Alternatives and similar medicines

Metformin is usually first-line for type 2 diabetes unless not tolerated or contraindicated. Other options include:

  • Sulfonylureas (e.g., glipizide, glimepiride, glyburide) - lower blood sugar by increasing insulin release. May cause hypoglycemia and weight gain.
  • Thiazolidinediones (e.g., pioglitazone) - improve insulin sensitivity. Watch for fluid retention and heart failure risk.
  • DPP-4 inhibitors (e.g., sitagliptin, linagliptin) - weight neutral; lower risk of hypoglycemia; brand-name in the USA.
  • SGLT2 inhibitors (e.g., empagliflozin, canagliflozin, dapagliflozin) - aid glucose excretion in urine; some have heart and kidney benefits; brand-name in the USA.
  • GLP-1 receptor agonists (e.g., semaglutide, liraglutide, dulaglutide) - injectable or oral; promote weight loss; brand-name in the USA.
  • Insulin (various types) - required in type 1 diabetes and may be used in type 2; risk of hypoglycemia; dosing individualized.
  • Alpha-glucosidase inhibitors (e.g., acarbose) - delay carbohydrate absorption; GI side effects are common.

Choice depends on goals, side effects, other conditions (heart, kidney), cost, and clinician guidance.

Compare typical out-of-pocket monthly costs in the USA (without insurance; prices vary by pharmacy, dose, and discounts):

  • Metformin generic: about $4 to $15 for many IR tablet supplies; ER forms may be $10 to $30.
  • Sulfonylureas generic: approximately $4 to $15.
  • Pioglitazone generic: roughly $10 to $25.
  • DPP-4 inhibitors (brand): often $400 to $600+.
  • SGLT2 inhibitors (brand): often $400 to $650+.
  • GLP-1 receptor agonists (brand): commonly $800 to $1,200+.
  • Insulin: highly variable; vials and pens can range from about $25 to several hundred dollars per month depending on product and supply.

Ask your pharmacist about generics, coupons, and patient-assistance programs.

Approximate prices in USD

In the USA, generic metformin is widely available and inexpensive at many pharmacies:

  • Immediate-release 500 mg, 60 to 90 tablets: often $4 to $15 cash price.
  • Immediate-release 850 mg or 1000 mg: commonly $6 to $20 depending on count.
  • Extended-release 500 mg or 750 mg: about $10 to $30+ depending on brand/generic and quantity.

Insurance, discount cards, and pharmacy selection can significantly change the final price. These are rough estimates only.

For what to do if cost is a barrier, see Legal and access in the USA.

More information

If you have questions about metformin, speak with your doctor, pharmacist, or diabetes educator. Metformin should be used only by the person for whom it was prescribed. Do not share your medication.

Routine tests may include kidney function, fasting blood glucose, A1c, and sometimes blood counts. Keep all medical and lab appointments.

If your readings are consistently too high or too low even when taking metformin as prescribed, contact your clinician.

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