Reviewed by a qualified healthcare professional. Updated May 2026. Written for patients and the general public in Australia and New Zealand.
| Detail | Information |
|---|---|
| Active ingredient | Metformin hydrochloride |
| Brand names in Australia | Diabex, Diaformin, Glucophage, Metex, Formet, Diabex XR, Metex XR, Diaformin XR |
| Drug class | Biguanide / oral antihyperglycaemic |
| Main uses | Type 2 diabetes; also used for PCOS |
| Available doses | 500 mg, 850 mg, 1000 mg (standard); 500 mg, 750 mg, 1000 mg (XR) |
| PBS patient co-payment | From ~$7.70 (concession) / ~$31.60 (general) per script |
| Prescription required? | Yes — Schedule 4 (S4), prescription only |
| How long to work | Blood sugar: 1–2 weeks; full benefit: 2–3 months |
| Take with food? | Yes — always take with or after a meal |
Metformin 500 mg is one of Australia’s most prescribed medicines. This guide explains what metformin treats, how it works, all available doses, PBS pricing, side effects, and what to expect if you are using it for weight loss or PCOS.
What is metformin?
Metformin (metformin hydrochloride) is an oral diabetes medicine in the biguanide drug class. It has been used since the 1950s and remains the recommended first-line pharmacological treatment for type 2 diabetes in Australia, as listed on the Pharmaceutical Benefits Scheme (PBS).
In Australia it is sold under several brand names — Diabex, Diaformin, and Glucophage being the most common — as well as numerous generics. All brands contain the same active ingredient and work identically.
How does metformin work?
Metformin lowers blood sugar through three main actions:
- Reduces glucose production in the liver. The liver normally releases glucose into the blood between meals. Metformin reduces this output, which is the primary driver of elevated fasting blood sugar in type 2 diabetes.
- Improves insulin sensitivity. Muscle and fat cells respond better to insulin and absorb more glucose from the blood.
- Slows glucose absorption. The gut absorbs carbohydrates more slowly after meals.
Importantly, metformin does not stimulate the pancreas to produce more insulin. This is why it rarely causes hypoglycaemia (dangerously low blood sugar) when used on its own, and why it does not typically cause weight gain — an advantage over some other diabetes medicines.
What is metformin used for?
Metformin is TGA-approved in Australia for type 2 diabetes mellitus in adults and in children aged 10 years and over, particularly when diet and exercise alone are insufficient. It can be used on its own or combined with other medicines, including insulin.
It is also widely prescribed for polycystic ovary syndrome (PCOS), where insulin resistance plays a central role. While this is technically an off-label use in Australia, it is strongly supported by clinical guidelines. Some doctors also prescribe it for pre-diabetes or alongside medicines such as empagliflozin or sitagliptin for people who need more than one agent to control their blood sugar.
Dosage — standard and XR tablets
Metformin is available as two tablet types. Standard-release tablets are taken two to three times a day with meals. Extended-release tablets (labelled XR) are taken once daily — usually with the evening meal — and are often better tolerated for stomach side effects.
Doses are always started low and increased gradually over several weeks to reduce digestive upset.
| Phase | Typical dose | Frequency |
|---|---|---|
| Starting dose | 500 mg | Once or twice daily with meals |
| After 1–2 weeks | 500–850 mg | Two to three times daily |
| Maintenance | 1000–2000 mg | Two to three times daily |
| Maximum dose | 3000 mg per day | Divided doses — only under medical guidance |
The choice of dose and tablet type should always be decided by your doctor. Do not adjust your dose without medical advice.
Price in Australia — PBS and private
Metformin is listed on the PBS, which means most Australians pay a subsidised co-payment at the pharmacy. Since September 2023, metformin has been eligible for 60-day PBS prescriptions, meaning eligible patients can receive a two-month supply on a single script.
| Patient type | Approximate cost per script | Notes |
|---|---|---|
| General (Medicare card) | ~$31.60 | Standard PBS co-payment 2026 |
| Concession (HCC / PBS Safety Net) | ~$7.70 | Pensioners and healthcare card holders |
| Private (no PBS) | ~$10–$25 per 100 tablets | Varies by brand and pharmacy |
Prices are indicative. Check with your pharmacist or the PBS website for current pricing.
How to get a prescription for metformin
Metformin is a Schedule 4 prescription-only medicine in Australia and cannot be purchased over the counter. A doctor must assess your health — usually including blood tests for blood glucose and kidney function — before prescribing it.
You can get a prescription through:
- Your regular GP — the most common route, especially for a new diagnosis or if you need blood tests.
- Telehealth — if you have an existing diagnosis and current test results, many Australian telehealth services can issue an electronic prescription (eScript) by phone or video.
- Online pharmacies — once you have a valid Australian eScript, it can be filled through a registered online pharmacy for home delivery.
If you are new to metformin, an in-person assessment is recommended so your doctor can review your kidney function before you start.
Side effects
Most people tolerate metformin well, particularly when the dose is increased gradually and taken with food. Side effects are most common in the first few weeks and tend to improve over time.
Common side effects (affect up to 30% of people)
- Nausea
- Diarrhoea
- Stomach cramping or discomfort
- Loss of appetite
- Metallic taste in the mouth
Taking metformin with food and starting on a low dose significantly reduces these effects. Switching to the XR formulation is another effective way to manage stomach side effects — ask your doctor if this could help you.
Less common but important
- Vitamin B12 deficiency — long-term use can reduce B12 absorption. Your doctor may monitor B12 levels over time and suggest a supplement if levels fall. See our article on Folic Acid for more on B vitamins.
- Lactic acidosis — a rare but potentially serious condition, most likely in people with kidney or liver problems or heavy alcohol use. Symptoms include unusual muscle pain, weakness, difficulty breathing, stomach discomfort, and feeling cold. This requires emergency medical attention.
Tell your doctor about all medicines you take. Metformin may need to be paused before surgery or before any imaging procedure using contrast dye (such as a CT scan), as it can affect kidney function in these situations. Consult your doctor before making any changes.
Metformin and weight loss
Metformin is not a weight-loss medicine, but modest weight loss is a commonly reported secondary effect — particularly in people with type 2 diabetes, pre-diabetes, or insulin resistance. By reducing insulin levels and improving how the body uses glucose, metformin can reduce fat storage and modestly decrease appetite.
Studies suggest an average weight reduction of around 2–3 kg over several months of consistent use. This is not dramatic, but it differs from many other diabetes medicines that cause weight gain. People who combine metformin with dietary changes and regular physical activity see greater results.
If weight management is a primary goal, speak to your doctor — other treatments may be more appropriate, either alongside or instead of metformin.
Metformin for PCOS
Polycystic ovary syndrome (PCOS) is closely linked to insulin resistance, and metformin is one of the most commonly prescribed treatments for it in Australia. By improving insulin sensitivity, metformin can help to:
- Regulate menstrual cycles
- Lower androgen (male hormone) levels, which can reduce excess hair growth and acne
- Support more regular ovulation, which may improve fertility
- Aid modest weight loss in overweight women with PCOS
Most women with PCOS begin to notice changes in menstrual regularity and other symptoms within 3 to 6 months of starting metformin. The XR formulation is generally preferred for PCOS as it causes fewer gastrointestinal side effects.
Metformin for PCOS should always be prescribed and monitored by a doctor or gynaecologist familiar with the condition.
Signs metformin is working
Because metformin works gradually, the signs can be subtle at first. Here is what to look for:
- Lower fasting blood sugar readings on a home glucometer — visible within 1–2 weeks of starting
- Lower HbA1c — your 3-month average blood sugar should fall by around 1–2% after 2–3 months on a stable dose
- Improved energy levels — better glucose control often reduces the fatigue associated with high blood sugar
- Modest weight loss — a gradual reduction over the first few months, particularly in people with insulin resistance
- More regular periods — for women with PCOS, menstrual cycles often become more predictable after 3–6 months
If you do not notice any of these signs after 3 months on a stable dose, speak to your doctor. A dose adjustment, an additional medicine, or a review of lifestyle factors may be needed.
Frequently asked questions
Can I take metformin with alcohol?
Occasional light drinking is generally acceptable, but regular or heavy alcohol use increases the risk of lactic acidosis — a rare but serious side effect. Alcohol also independently affects blood sugar. Speak to your doctor about your individual risk.
When is the best time to take metformin 500 mg once a day?
Take it with your largest meal of the day — most commonly the evening meal. Taking metformin with food significantly reduces stomach side effects. For the XR formulation, evening dosing is usually recommended.
Is 500 mg of metformin a low dose?
Yes. 500 mg once or twice daily is the standard starting dose, used to minimise digestive side effects. Most adults gradually increase to 1000–2000 mg per day. Your doctor will determine the right maintenance dose based on your blood sugar response and kidney function.
What is the difference between metformin XR and standard metformin?
Metformin XR (extended-release) releases the medicine slowly, reducing nausea and diarrhoea. It is taken once daily. Standard-release metformin acts faster but requires dosing 2–3 times a day. Both types are equally effective at controlling blood sugar.
What foods should I avoid while taking metformin?
There are no strict food restrictions, but high-sugar and high-carbohydrate foods work against the medicine’s effect on blood sugar. A diet rich in vegetables, lean protein, and whole grains supports better results. Taking metformin with a meal also reduces stomach side effects.
How long does metformin take to work?
Metformin begins to lower blood sugar within the first 1–2 weeks. Full effects on HbA1c (your 3-month average blood sugar) are usually seen after 2–3 months on a stable dose. For PCOS symptoms such as menstrual regularity, allow 3–6 months.
Can metformin be used during pregnancy?
Metformin is sometimes used during pregnancy to manage gestational diabetes or in women with PCOS, but only under close medical supervision. Insulin remains the standard treatment for diabetes in pregnancy in Australia. Always consult your doctor if you are pregnant or planning to conceive.
Does metformin interact with other medicines?
Metformin can interact with certain medicines that affect kidney function, including some contrast dyes used in imaging, and some heart medicines. Always tell your doctor and pharmacist about all medicines, supplements, and herbal products you take.
This article provides general information only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before starting, stopping, or changing any medication. For emergencies, call 000.
Articles in the Medication section are written for patients and the general public in Australia and New Zealand, and reviewed by a qualified healthcare professional under the editorial leadership of Dr Srinivas Bolisetty PSM, MD, FRACP. ANMF does not accept sponsorship or funding from pharmaceutical or commercial organisations.