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

To date (2022), the Therapeutic Goods Administration of Australia has approved the use of 5 different medications for weight loss – phentermine, orlistat, bupropion/naltrexone, liraglutide and the recently approved semaglutide. 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 5-10% of total body weight. For some people it is less than this, for some it is more (20% or greater). New medications are currently being developed and tested that show even better results to the ones we currently have available, making this a very exciting area of medicine.

Quick Info

  • 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.

Weight loss medications currently available in Australia

Phentermine 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.

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.

Liraglutide is a glucagon-like peptide 1 (GLP-1) agonist initially developed to treat Type 2 diabetes, but now approved in Australia for weight loss. Liraglutide is self-administered by once daily subcutaneous injection. It effects gut hormones resulting in reduced hunger and increased satiety. This class of medication is generally well tolerated. Side effects may include nausea, abdominal cramps and change in bowels. Liraglutide-induced weight loss may be associated with increased incidence of symptomatic gallstones, and more rarely, pancreatitis.

Semaglutide is also a GLP-1 agonist developed to treat Type 2 diabetes. It has a longer half life than liraglutide and therefore only needs to be injected once a week. The side effect profile and tolerability are similar to liraglutide. It has been used in low doses “off Label” in Australia for quite some time now. It has recently been approved at a higher dose for weight loss, but supply issues have limited accessibility.

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.