What Is Metformin?
Metformin (brand names: Glucophage, Glumetza) lowers blood sugar by reducing glucose production in the liver and improving insulin sensitivity. It is almost always the first medication prescribed for type 2 diabetes.
How it lowers blood sugar
Metformin works in three ways: (1) reduces liver glucose output by ~30%, (2) increases muscle glucose uptake, (3) slows intestinal glucose absorption. It does NOT cause hypoglycaemia on its own.
Standard Dosing Schedule
| Phase | Dose | Timing |
|---|---|---|
| Week 1–2 | 500 mg | Once daily with evening meal |
| Week 3–4 | 500 mg | Twice daily (morning + evening) |
| Week 5+ | 1000 mg | Twice daily (target dose) |
| Maximum | 2550 mg | Split across 3 meals |
Blood Tests to Monitor on Metformin
| Test | Frequency | Why |
|---|---|---|
| HbA1c | Every 3–6 months | Check diabetes control |
| eGFR (kidney function) | Every 6–12 months | Metformin is stopped if eGFR <30 |
| Vitamin B12 | Annually | Metformin reduces B12 absorption |
| Liver function | Annually | Baseline + monitoring |
| FBC | Annually | Check for macrocytic anaemia from B12 deficiency |
Common Side Effects
- Nausea, stomach upset (most common — usually improves after 2–4 weeks)
- Diarrhoea especially when starting
- Metallic taste
- Loss of appetite
- Vitamin B12 deficiency with long-term use
Stop Metformin and seek urgent care if you haveSevere muscle pain, weakness, difficulty breathing, or abdominal pain — these can be signs of lactic acidosis, a rare but serious complication.
When Metformin Must Be Stopped
| Situation | Reason |
|---|---|
| eGFR <30 mL/min | Risk of lactic acidosis |
| Contrast dye (CT scan) | Withhold 48 hours before and after |
| Surgery | Withhold day before and day of |
| Acute illness / dehydration | Increases lactic acidosis risk |
| Excessive alcohol | Alcohol + metformin raises lactic acid risk |
B12 TipIf you've been on metformin for more than 1 year, ask your doctor to check your Vitamin B12 level. Deficiency is common and easily treated with supplements.
Metformin and Weight Loss
Metformin often causes modest weight loss (1–3 kg) as a side effect, mainly due to reduced appetite and lower calorie absorption. It is not a weight-loss drug but this side effect is considered beneficial in overweight patients with type 2 diabetes.
Can I drink alcohol on metformin?
Light-to-moderate drinking is generally safe, but heavy drinking significantly increases the risk of lactic acidosis. Your doctor may advise avoiding alcohol entirely.
Does metformin cause low blood sugar?
On its own, metformin does not cause hypoglycaemia. Low blood sugar can occur if combined with insulin or sulfonylureas like glipizide.
Can I take metformin if my kidneys are not perfect?
Metformin is safe when eGFR is 45–89. Dose is halved at eGFR 30–44, and stopped completely below eGFR 30.
Does metformin affect the heart?
Yes — favourably. Metformin has been shown to reduce heart attack risk and cardiovascular mortality, independently of its blood sugar effects.
Why does metformin cause stomach problems?
Metformin irritates the gut lining. Taking it with food, starting at a low dose, and using the extended-release (XR) form greatly reduces GI side effects.
Medical Disclaimer: This page is for general education only and does not replace professional medical advice. Always consult a qualified healthcare provider.