Metformin is not approved for weight loss in Australia. The TGA approves it to treat type 2 diabetes, and its product information says people taking it had either a stable body weight or modest weight loss. In the largest trial, the average loss was about 2 kg. Prescribing it for weight alone is an off-label decision for a doctor.
People search for metformin and weight loss for good reasons. Weight and blood sugar are tangled together, and metformin is cheap and familiar. This guide sets out what the Australian product information, the PBS and the trials say.
| What the Australian sources say | |
|---|---|
| Approved use (TGA) | Type 2 diabetes in adults and children from 10 years, particularly in overweight patients, when diet and exercise alone have not controlled glucose |
| Approved for weight loss? | No. Any use for weight alone is off-label and a prescriber's decision |
| PBS | Listed on the General Schedule as an unrestricted benefit: 500 mg, 850 mg and 1 g tablets, and 500 mg and 1 g extended-release tablets |
| Weight effect in the product information | Either a stable body weight or modest weight loss |
| Very common side effects | Diarrhoea, nausea, vomiting, abdominal pain and loss of appetite, mostly when starting |
| Monitoring | Kidney function, and vitamin B12 every year |
| Rare but serious | Lactic acidosis, mainly with poor kidney function |
Metformin is a tablet that lowers blood glucose. It has been used for type 2 diabetes for decades and is sold in Australia under brand names such as Diabex and Diabex XR, as well as generic versions.
It works in a few places at once. The product information describes it reducing the amount of glucose the liver releases, helping muscles take up glucose, and changing how the gut handles glucose, including a rise in GLP-1, one of the gut's own fullness hormones. It does not make the pancreas release more insulin, which is why it does not cause low blood sugar when taken on its own.
On the PBS, metformin is an unrestricted benefit. The TGA-approved use is type 2 diabetes. Using it for anything else, including weight, is off-label prescribing, which is legal in Australia but rests on the doctor's judgement for that person.
Metformin helps some people lose a small amount of weight, and the average loss in trials is modest. The best evidence comes from the US Diabetes Prevention Program (DPP), which followed adults with raised blood glucose for more than 15 years.
In the original trial, published in the New England Journal of Medicine in 2002, 3,234 adults with prediabetes and an average BMI of 34 were randomly assigned to metformin, a lifestyle program or placebo. Over about three years, average weight loss was 2.1 kg with metformin, 5.6 kg with the lifestyle program and 0.1 kg with placebo.
The lifestyle program also did more to prevent diabetes. It cut new cases by 58% against placebo, and metformin by 31%.
In the long-term follow-up (DPP Research Group, Diabetes Care, 2012), people on metformin weighed about 2% less than at the start, and those who kept taking it kept the loss. That held for at least 10 years.
You may have read that metformin users lost 6.2% of their body weight over 15 years. That figure comes from a 2019 analysis (Apolzan and colleagues, Annals of Internal Medicine) of a subgroup: the 28.5% of the metformin group who had already lost at least 5% in the first year. Among them, the loss held at 6.2% between years 6 and 15. It does not describe what happened to most people taking metformin.
For polycystic ovary syndrome, the 2023 international guideline led from Monash University says metformin alone should be considered in adults with PCOS and a BMI of 25 or more, for body measurements and metabolic outcomes such as insulin resistance, glucose and lipids. The same guideline says women should be told that metformin and an active lifestyle program have similar effects. You can read more in our guide to PCOS and insulin resistance.
Yes, 500 mg is the smallest tablet strength and the usual starting dose in the product information, but that dosing is for type 2 diabetes. The Diabex product information says adults start on 500 mg once or twice a day with meals, increased over a few weeks if needed, up to a maximum of 1 g three times a day.
There is no approved weight-loss dose, because weight loss is not an approved use. Any dose for anything other than type 2 diabetes is a decision between you and the doctor prescribing it.
The product information also says the tablets are taken in divided doses with meals, and that a full assessment of the response should not be made before day 21 of treatment.
Gut side effects are the most common. The product information lists diarrhoea, nausea, vomiting, abdominal pain and loss of appetite as very common, mostly at the start, and says they usually settle. A change in taste is common.
Long-term use can lower vitamin B12, and the product information recommends checking B12 every year. Low B12 can cause tiredness, anaemia and nerve symptoms, so it is worth knowing your level. A vitamin B12 test and a kidney function test are part of normal monitoring.
The most serious risk is lactic acidosis, which is very rare but can be life-threatening. The Diabex product information lists the main risk factors as poor kidney function, older age and doses above 2 g a day, and lists metformin as unsuitable for people with:
The product information also lists drinking to the point of intoxication as an inadvisable combination, because it raises the risk of lactic acidosis. Metformin interacts with some other medicines too, including some diuretics, and your doctor and pharmacist will check these.
Metformin and the newer weight-loss injections are different medicines with different approvals. Semaglutide (Wegovy), liraglutide (Saxenda) and tirzepatide (Mounjaro) are approved by the TGA for chronic weight management in some adults, alongside diet and activity. Metformin is not.
They also work differently. GLP-1 medicines act directly on appetite signals in the brain and gut, and are given by injection. Metformin is a tablet whose main job is lowering glucose. Our guide to weight-loss medication in Australia covers the approved options, and our Ozempic guide explains how semaglutide works.
Metformin's effect on weight runs through glucose and insulin, so it is worth knowing where yours sit first. Insulin resistance makes weight harder to shift, and it can sit behind normal glucose results for years.
“Insulin resistance tends to precede glucose impairment by about 10-15 years, but it is not routinely looked for in modern general practice and is rarely highlighted by doctors. Addressing hyper-insulinemia, before glucose becomes impaired, is ideal and optimal when it comes to prevention.”
Dr Michelle Woolhouse, Vively Medical Director
Three markers show where you sit. HbA1c reflects your average glucose over the last two to three months. Fasting insulin and HOMA-IR show how hard your body is working to keep glucose there. Our optimal ranges are HbA1c 4.0 to 5.3%, fasting insulin 3 to 5 mIU/L and HOMA-IR 1.0 or below. If you already have fasting glucose and insulin results, the HOMA-IR calculator works out your score.
Among Vively members who don't have type 2 diabetes, HbA1c above our optimal limit of 5.3% went from about 1 in 10 under 30 to 4 in 10 women and half of men aged 60 and over. Observational member data, not a controlled study.
% with HbA1c above 5.3% (the Vively optimal limit)
| Women | Men | |
|---|---|---|
| 18 to 29 | 11% (n=267) | 10% (n=263) |
| 30 to 39 | 13% (n=990) | 16% (n=649) |
| 40 to 49 | 15% (n=1,170) | 26% (n=704) |
| 50 to 59 | 30% (n=866) | 32% (n=414) |
| 60+ | 41% (n=501) | 50% (n=261) |
% with HbA1c 6.0% or higher
| Women | Men | |
|---|---|---|
| 18 to 29 | 0% (n=267) | 1% (n=263) |
| 30 to 39 | 1% (n=990) | 1% (n=649) |
| 40 to 49 | 1% (n=1,170) | 2% (n=704) |
| 50 to 59 | 4% (n=866) | 5% (n=414) |
| 60+ | 6% (n=501) | 13% (n=261) |
That drift with age is common, and it is where food, movement, sleep and stress do the most good. In the DPP, the lifestyle program beat metformin on both diabetes prevention and weight.
“The health system doesn't focus on health. Lifestyle is the root cause of health. Most chronic diseases are lifestyle driven.”
Dr Michelle Woolhouse, Vively Medical Director
We don't prescribe metformin or weight-loss medicines. We help you see what is going on underneath. The Baseline Health Check measures 70+ markers, including HbA1c, fasting glucose, fasting insulin, HOMA-IR, vitamin B12 and kidney function, read against optimal ranges. A practitioner explains your results, our dietitians can help you build a food and activity plan that suits your life, and your membership includes a targeted re-test after 3 months so you can see the trend. For a closer look at weight-related markers, members can add the Weight Management Test.
The Baseline Health Check measures 70+ markers, including HbA1c, fasting insulin and HOMA-IR, from one blood draw at one of 3,700+ partner collection centres, with a practitioner to explain them.
Modestly, on average. In the Diabetes Prevention Program, people with prediabetes on metformin lost 2.1 kg over about three years, against 5.6 kg with a lifestyle program and 0.1 kg with placebo. The Australian product information describes either a stable weight or modest weight loss. It is not approved for weight loss.
500 mg is the lowest tablet strength and the usual starting dose for type 2 diabetes in the Australian product information, which goes up to 3 g a day. There is no approved dose for weight loss, because weight loss is not an approved use. Any off-label dose is your prescriber's decision.
A doctor can prescribe a medicine off-label if they judge it appropriate for you, but metformin is not TGA-approved for weight loss. Medicines that are approved for weight management include semaglutide (Wegovy), liraglutide (Saxenda) and tirzepatide (Mounjaro). Your GP can explain which, if any, suit you.
With meals. The Australian product information says the tablets are taken in divided doses with meals, which also eases gut side effects. Extended-release versions have their own instructions. Follow the directions from your prescriber and pharmacist rather than general advice online.
It can. Low vitamin B12 is listed as a common side effect, and the risk rises with higher doses and longer use. The Australian product information recommends checking B12 levels every year for people taking metformin. A simple blood test does it, and your GP can add it to your usual diabetes checks.
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Vively is a general wellness platform and does not provide medical advice, diagnosis, or treatment. Any information, insights or guidance offered through our app, website, programs, or coaches is for educational and informational purposes only and should not be considered a substitute for professional medical advice or care. Always consult a qualified healthcare provider before making any health-related decisions.
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