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Brand example: Glucophage. Active pharmaceutical ingredient: metformin. Primary use: first-line oral treatment for type 2 diabetes mellitus in adults to be used alongside dietary and lifestyle measures; it can be combined with other glucose-lowering medicines when required.

In the United Kingdom metformin is typically supplied as a prescription-only medicine. For quick navigation: see administration notes at How to administer metformin, urgent safety signals at Advisories and urgent signs, or supply information at Understanding United Kingdom status under law plus the steps to obtain it..

The way metformin functions to lower blood sugar and when it is indicated

Metformin is a biguanide glucose-lowering medicine. It reduces blood sugar by several complementary actions:

  • Lowering glucose production in the liver.
  • Improving insulin sensitivity in peripheral tissues so muscles and fat use more glucose.
  • Reducing absorption of glucose from the gut to a small extent.

Because metformin does not stimulate insulin secretion, it has a low intrinsic risk of causing hypoglycaemia when used alone. It is commonly selected as the initial pharmacological therapy for type 2 diabetes after lifestyle measures are insufficient to control glucose.

Prescribers may also use metformin in specific metabolic conditions or polycystic ovary syndrome in some cases; follow specialist advice for these signs that point to.

Dose regimen details for the available strengths details

Multiple manufacturers supply metformin in immediate-release and modified-release forms in the UK. Standard tablet strengths you are likely to see include 250 mg, 500 mg, 850 mg and 1000 mg.

  • Immediate-release: commonly started at 500 mg twice daily or 850 mg once daily with food, in conjunction with then increased gradually while time sensitive monitoring tolerance and blood tests.
  • Modified-release (MR or XL): usually given once daily, often with the main evening meal to reduce stomach upset.

Maximum total daily doses vary by formulation and patient factors. Some immediate-release regimens reach up to about 2550 mg per day in selected people, while MR formulations often have different maxima. Those with impaired kidney function will have lower recommended limits. For switching between formulations see Tips on taking metformin.

How metformin should be taken

Only take metformin exactly as prescribed for you. Do not share your medication.

  • Immediate-release tablets: take with or immediately after food to lessen gastrointestinal medication side effects.
  • Modified-release tablets: swallow whole; do not crush, split or chew MR tablets unless the product information specifically permits it.
  • Attend scheduled blood tests so your prescriber can check kidney function (for example eGFR) and glucose control.
  • If you are planning to move from twice-daily immediate-release to a once-daily MR product, obtain clinical advice to ensure an appropriate conversion and dose.

If your treatment is adjusted or you develop new symptoms, contact your prescriber or community pharmacist before changing doses. For missed tablets read Remedies for a omitted dose.

Be advised and urgent signs

Accumulation of metformin can rarely cause lactic acidosis, a serious and possibilitiesly life-threatening condition. Seek urgent medical assessment if you develop any combination of the following features:

  • Marked weakness or profound tiredness
  • Breathlessness or unusually fast breathing
  • Woozy feeling, fainting or feeling unusually cold
  • Severe muscle pain or unexplained severe abdominal pain
  • Persistent nausea and vomiting

Metformin alone usually does not produce low blood sugar, but the risk rises if you are also taking insulin or sulfonylureas. Keep fast-acting carbohydrate handy and follow any hypoglycaemia action plan you have been given.

Avoid heavy or binge drinking because alcohol increases the risk of lactic acidosis and may destabilise glucose control. You may be advised to stop metformin temporarily before and after procedures that use iodinated contrast or before major surgery; follow the specific instructions provided by your healthcare team.

Absolute exclusions for therapy and important cautions

Do not start or continue metformin unless a clinician has assessed you if any of the following apply:

  • Known allergy to metformin or any ingredient in the product
  • Severe or acute kidney impairment
  • Current diabetic ketoacidosis or hyperosmolar hyperglycaemic state
  • Severe liver disorder
  • Unstable or severe heart failure, recent heart attack, or severe respiratory disease
  • Severe infection, dehydration or shock
  • Alcoholic drink product misuse or dependence
  • Very low calorie intake, for example less than 1000 kcal per day
  • Prior lactic acidosis thought to be related to metformin
  • Prenatal care and breastfeeding support unless advised by your clinician

Older people and those who do heavy physical work should have an individualized risk assessment before treatment. Discuss any concerns by consulting your prescriber.

Negative reactions and constant monitoring

The most frequently reported deleterious effects are gastrointestinal and often settle over time:

  • Nausea, sometimes with vomiting
  • Diarrhoea symptoms, wind or bloating
  • Decreased appetite or abdominal discomfort
  • Small fluctuations in weight for some people

Allergic reactions, for example rash or facial swelling, are uncommon but require prompt assessment. If you suspect lactic acidosis or any severe reaction see Alert signals and urgent signs and get emergency help.

Your clinician will usually check kidney function before starting and periodically thereafter. Report any new breathlessness, persistent vomiting or collapse without delay.

Partnered social interpersonal dialogue and exchanges influence perceptions and decisions. with medicines and other substances

Tell your healthcare team about all medicines, over-the-counter products, vitamins and herbal remedies. Noteworthy exchanges include:

  • Cimetidine as a treatment for ulcers and GERD: may raise metformin blood levels and require metric monitoring.
  • Beverage that contains ethanol: increases lactic acidosis risk and can destabilise blood glucose.
  • Diuretics, especially thiazides: can affect renal function and glucose metabolism.
  • Insulin and sulfonylureas: increase hypoglycaemia risk when used with metformin; dose adjustments may be needed.
  • Certain antibiotics, corticosteroids and sympathomimetics: can influence blood glucose and warrant time sensitive monitoring.

If you are booked for imaging that uses iodinated contrast, follow local guidance about pausing metformin; see Cautions and urgent signs for further facts and figures.

Guidance for missing a dose

  • If you forget to take a dose, take it right away when you remember, unless the next dose is due soon.
  • Do not exceed the prescribed dose to cover a missed tablet.
  • Resume your normal schedule at the next planned time.

If you miss doses frequently, speak with your pharmacist about reminder systems or whether a once-daily MR product could improve adherence. For serious dosing errors see Emergency actions in overdose on medicine cases.

In an overdose death reaction profile procedures and emergency actions

An an opioid overdose of metformin can cause severe illness. Early symptoms often include marked nausea, vomiting and abdominal pain. In large an opioid overdoses lactic acidosis can develop, which presents with fast breathing, extreme weakness, dizziness or loss of consciousness. If an opioid overdose is suspected seek immediate emergency medical care.

If you are taking other glucose-lowering medicines and develop hypoglycaemia signs such as sweating, trembling or confusionplease audit this. your blood glucose and follow your hypoglycaemia plan. For severe or persistent hypoglycaemia contact emergency services.

Preserve and handle

  • Store metformin at normal room temperature, typically between 20 and 25 C.
  • Protect the medicine from excessive heat, moisture and direct sunlight.
  • Do not keep medicines in bathrooms. Keep every medicine out of a child's reach and out of sight.

Contingent options with rough cost range in the United Kingdom

Private prices vary with supplier, pack size and dose. The ranges below are indicative in GBP and should be treated as approximate.

Typical metformin cost examples

  • Generic metformin immediate-release 500 mg: roughly 1 to 6 GBP for common 28 to 56 tablet packs.
  • Metformin modified-release: around 5 to 20 GBP per month depending on dose and pack size.

Other glucose-lowering options (indicative private monthly costs)

  • Sulfonylureas (gliclazide, glimepiride): inexpensive generics, about 2 to 6 GBP per month; higher risk of low blood sugar.
  • DPP-4 inhibitors (sitagliptin, linagliptin): typically 20 to 40 GBP per month.
  • SGLT2 inhibitors (empagliflozin, dapagliflozin): commonly 20 to 50 GBP per month; may provide heart and kidney benefits for selected patients.
  • Pioglitazone: usually low cost but not recommended in people with heart failure.
  • GLP-1 receptor agonists (semaglutide, dulaglutide): often much more expensive, commonly from 70 GBP per month and usually injectable.
  • Insulin: cost and regimen vary considerably; requires tailored prescribing and ongoing supervision and monitoring.

Choice of therapy takes into account kidney function, cardiovascular status, weight goals, side effect profiles and patient preference. Discuss likely costs and options with your prescriber or community pharmacy. Practical administration advice is at Best practices for taking metformin and safety reminders are at Cautionary notes and urgent signs.

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