💊 Medication Guide

Biguanide / Blood glucose-lowering agent

Metformin

The most prescribed medication for type 2 diabetes and insulin resistance.

Metformin is the first-line medication for type 2 diabetes worldwide. It is also used for prediabetes, PCOS, and insulin resistance. It is safe, effective, inexpensive, and has been in use for over 60 years.

What It Is Used For

✓ Type 2 diabetes

✓ Prediabetes (to delay progression)

✓ PCOS (insulin resistance)

✓ Gestational diabetes (with medical supervision)

How It Works

Metformin works primarily by reducing the amount of glucose the liver releases into the bloodstream. It also makes muscle cells more sensitive to insulin, allowing glucose to be used more efficiently. Unlike some other diabetes medications, metformin does not cause weight gain and does not cause low blood sugar (hypoglycaemia) when used alone.

Dosing — Typical Guidance

Starting dose

500mg once or twice daily with meals — started low to reduce stomach side effects

Maintenance dose

500mg–1000mg twice daily with meals (maximum 2550mg/day)

Extended-release (XR)

Often better tolerated — taken once daily with the evening meal

Adjustment

Dose is increased gradually over weeks — do not self-adjust

Side Effects

Common

Nausea, diarrhoea, stomach discomfort — especially when starting. Usually improves within 2–4 weeks. Taking with food helps significantly.

Continue taking, inform your doctor if persistent.

Common

Metallic taste in the mouth — usually temporary

Generally resolves — no action needed.

Serious (Rare)

Lactic acidosis — very rare, more likely in kidney disease. Symptoms: unusual muscle pain, difficulty breathing, stomach pain, dizziness, cold or blue feeling.

Stop metformin and seek emergency care immediately.

Rare

Vitamin B12 deficiency with long-term use — may cause nerve tingling or fatigue

Annual B12 level check if on metformin long-term. B12 supplements if deficient.

Who Should Avoid This Medication

Who Should Not Take This (or Use With Caution)

⚠️ People with significant kidney disease (eGFR below 30) — metformin accumulates
⚠️ Acute illness causing dehydration — temporary hold may be needed
⚠️ Before major surgery or procedures using contrast dye — discuss with your doctor
⚠️ Excessive alcohol use — increases lactic acidosis risk

Drug Interactions to Know

Medication / Substance	Why It Matters
Alcohol	Increases risk of lactic acidosis. Avoid excessive alcohol while taking metformin.
Contrast dye (for CT scans)	Metformin should usually be stopped 48 hours before iodinated contrast. Tell your doctor or radiologist you take metformin before any scan.
Certain diuretics (water tablets)	May affect kidney function, which affects metformin clearance. Blood tests may be needed.

Monitoring While on This Medication

HbA1c

Every 3 months initially, then every 6 months once stable

Kidney function (eGFR)

Annually — or more often if borderline kidney function

Vitamin B12 level

Annually if on metformin for more than 3 years

Blood pressure and weight

At every clinic visit

Frequently Asked Questions

Will metformin make me lose weight?

Metformin is weight-neutral to mildly weight-reducing. It does not cause the weight gain associated with some other diabetes medications. It is not primarily a weight loss drug.

Does metformin cause low blood sugar?

No — not when used alone. Metformin does not stimulate insulin production. Low blood sugar (hypoglycaemia) only becomes a risk if metformin is combined with insulin or insulin-stimulating medications.

Can I take metformin during pregnancy?

Metformin is used in some cases of gestational diabetes and PCOS in pregnancy under medical supervision. It crosses the placenta. Always discuss with your doctor — do not start or stop during pregnancy without medical guidance.

How long will I need to take metformin?

Metformin is a long-term medication for most people with type 2 diabetes. With significant lifestyle changes (diet, exercise, weight loss), some people with prediabetes or early diabetes are able to reduce or stop — always under medical supervision.

Is metformin safe for the kidneys?

Metformin is generally safe for kidneys — in fact, it is preferred because it is one of the few diabetes medications that does not worsen kidney disease. However, it is not recommended if kidney function is already significantly impaired (eGFR below 30).