Obesity is a chronic, relapsing disease and should be managed as such. Along with lifestyle intervention, pharmacotherapy (medications) can be a useful tool in effecting and maintaining clinically meaningful weight loss. Pharmacotherapy should be considered in those with BMI >30kg/m2 or those with BMI >27-30 kg/m2 with obesity related complications. Pharmacotherapy can be used in both patients that have never had weight loss surgery, as well as those that have. In those that have had weight loss surgery, the use of medications may be useful in cases of insufficient weight loss, as well as those that have experienced weight regain.

The use of medications for weight loss

In Australia the Therapeutic Goods Administration (TGA) has approved the use of several different medications for weight loss – terzepatide, semaglutide, liraglutide, phentermine, orlistat, and bupropion/naltrexone. There are also other medications that have been proven to be successful weight loss medications, that are not TGA approved for weight loss in Australia. They are therefore sometimes prescribed “off label” for weight loss.

The use of medications for weight loss is not a ‘one size fits all’ process. Treatment is individualised to the patient and results will vary from person to person. The average weight loss achieved in patients taking weight loss medications is 5-15% of total body weight. For some people it is less than this, for some it is more (20% or greater).

While generally well tolerated, weight loss medications do have some limitations- cost, potential side effects, contraindications (such as pregnancy), and the possibility of weight regain when the medications are stopped. Evidence shows that the long -term use of weight medications is safe in the majority of patients. Therefore some patients may stay on therapy long term, while others use it for a shorter duration to aid weight loss while building good long term lifestyle habits.

  • Pharmacotherapy can be a useful tool in effecting and maintaining clinically meaningful weight loss.

  • The use of medications for weight loss is not a ‘one size fits all’ process.

  • Treatment is  individualised to the patient and results will vary.

  • New medications are currently being developed and tested that show even better results to the ones currently available.

Quick Info

Weight loss medications currently available in Australia

Semaglutide (Ozempic or Wegovy) is a GLP-1 agonist originally developed to treat Type 2 diabetes. It is administered by once weekly injection with gradual dose increase. It decreases hunger, increases satiety, delays gastric emptying and supports glycaemic control. Possible side effects include nausea, constipation / diarrhoea and fatigue. There is also a rare risk of pancreatitis and gallbladder issues. Gallstone formation can occur with any form of rapid weight loss and is not specific to this class of medication.

Terzepatide (Mounjaro) is a dual GIP/ GLP1 receptor agonist, meaning it works on two receptors rather than one. It may therefore have stronger appetite control and metabolic effects. It is also administered by weekly injection and has a similar side effect profile to semaglutide.

Liraglutide (Saxenda) is also a GIP1 receptor against. But unlike semaglutide or terzepatide, it needs to be injected daily and has a more modest effect on weight. Generic liraglutide is now available in Australia, reducing the monthly cost. The Saxenda brand was discontinued in Australia in December 2025.

Phentermine (Duromine / Metermine) is a sympathomimetic agent that suppresses appetite. It has been available in Australia for decades. Common side effects include dry mouth, disturbed sleep, irritability/ agitation, increased blood pressure and increased heart rate. Given the effects of phentermine on the cardiovascular system, it should not be used in people with a history of cardiovascular disease. It should also not be used in patients with significant anxiety disorders, over-active thyroid, a history of drug or alcohol dependence, pregnancy, or breast-feeding.

Orlistat inhibits the production of pancreatic and gastric lipase and therefore reduces absorption of dietary fat. Side effects are due to fat malabsorption and may include diarrhoea, flatulence, faecal incontinence, and fat-soluble vitamin deficiencies. These side effects may be limited by adhering to a low fat, high fibre diet.

Naltrexone / Bupropion (Contrave) is an orally administered weight loss medication. The combination of an opioid antagonist (naltrexone) and a dopamine and noradrenaline re uptake inhibitor (bupropion) works centrally on the brain to reduce hunger and cravings. Common side effects include nausea with or without vomiting, headache, dizziness, and constipation. Serious side effects may include seizures, allergic reactions and change in mood.

Topiramate is an anti-convulsant used to treat seizures and help prevent migraines. It has been used off label to treat obesity. In the US, it is available as a combination tablet with phentermine. Such a combination does not exist in Australia. Dose-related side effects may include dry mouth, altered taste, constipation, disturbed sleep, dizziness, decreased concentration and attention, and memory impairment. Rare but serious side effects include closed angle glaucoma and increased suicidal thoughts. Topiramate should not be used in patients with a history of renal stones or glaucoma, or in pregnancy.