Contrave vs Mounjaro in Australia

No randomised trial has compared naltrexone and bupropion with tirzepatide or any other GLP-1 medicine; a Europe PMC search of randomised trials on 6 October 2026 returned placebo-controlled trials and post-hoc analyses only.

The Contrave figures below are from the Australian Product Information, which uses the intention-to-treat set; the journal papers report slightly larger numbers from a modified analysis (COR-I 6.1% against 1.3%). The Mounjaro figures are from SURMOUNT-1, the placebo-controlled trial in people without diabetes.

The wording here is from the Australian Product Information and Consumer Medicine Information for each medicine, not the American labels, which carry a boxed suicidality warning for Contrave and a boxed thyroid warning for tirzepatide that the Australian documents do not.

Contrave has 13 contraindications: uncontrolled high blood pressure; any seizure disorder or history of seizures; a central nervous system tumour; acute withdrawal from alcohol or benzodiazepines; a history of bipolar disorder; any other bupropion or naltrexone product; a current or previous diagnosis of bulimia or anorexia nervosa; current opioid dependence, use of opioid-containing medicines, treatment with methadone or buprenorphine, or acute opioid withdrawal; a monoamine oxidase inhibitor within 14 days; pregnancy; severe liver disease; end-stage kidney failure; and allergy to either ingredient. The Consumer Medicine Information says opioids must have been stopped for at least 7 to 10 days before starting, and Contrave must be stopped at least 3 days before any planned opioid treatment such as surgery. It is not recommended after a recent heart attack, in unstable heart disease or class III or IV heart failure, under 18, over 75 or in mild or moderate liver impairment.

Mounjaro has one contraindication: allergy to tirzepatide or any ingredient. Its document lists cautions rather than bans: a history of pancreatitis, severe gut disease including gastroparesis, diabetic eye disease, kidney impairment with severe gut symptoms, a history of suicidal thoughts, and delayed stomach emptying before general anaesthesia.

What to expect in the first months: Contrave's common effects are nausea, constipation and vomiting (trial rates in the table above), plus headache, dizziness, dry mouth, insomnia, anxiety and palpitations. Most nausea starts within four weeks; the Product Information says the majority of cases resolved within four weeks and almost all by week 24. Mounjaro's are nausea, diarrhoea (18.7% to 22.5% against 7.8% on placebo), constipation, vomiting and decreased appetite, clustering around each dose increase; its document says to consider a dose change or stopping if severe gut symptoms develop.

Symptoms that need urgent medical attention, from each Consumer Medicine Information leaflet. Contrave: a seizure; wheezing, swelling of the lips, mouth or eyelids, or difficulty breathing; suicidal thoughts, hostility, panic or agitation; a widespread rash with fever or blistering; bleeding from the rectum; yellowing of the skin or eyes. Mounjaro: severe persistent pain in the stomach and back with vomiting (possible pancreatitis); rash, rapid swelling of the face, mouth or throat, or trouble breathing; sudden severe upper abdominal pain, fever or jaundice (gallbladder); any change in or loss of vision. The Mounjaro leaflet says to tell your doctor as soon as possible about severe abdominal pain with bloating and constipation (possible bowel blockage).

Both are Schedule 4 prescription-only medicines. Contrave (iNova Pharmaceuticals) has been on the Australian Register of Therapeutic Goods since 24 August 2018 and on sale since February 2019; it is the only combination tablet registered here for weight management, the other oral options being orlistat and phentermine. Mounjaro (Eli Lilly) has been registered for type 2 diabetes since December 2022, chronic weight management since September 2024 and obstructive sleep apnoea with obesity since June 2025.

A GP, a specialist or a nurse practitioner can prescribe either. Both Product Information documents set the same starting criteria: a BMI of 30 or more, or 27 to 30 with at least one weight-related condition, alongside a reduced-energy diet and more physical activity. Contrave's adds the contraindications above, the 16-week rule, an annual cardiovascular risk assessment before continuing past a year (added in the September 2026 revision), and a requirement that every prescriber has received the sponsor's physician educational material.

Some telehealth services prescribe Contrave: Weight Loss GP (August 2026) offers it after a telehealth assessment and quotes $230 to $260 a month, its own figure. For Mounjaro, Juniper, Hims, Moshy, Mosh, Youly, hub.health and InstantScripts sell monthly weight-loss programs that do not state which medicine or dose they cover. In September 2026 Lilly opened LillyDirect, where an e-script from your own doctor is sent to a partner pharmacy that dispenses and delivers; Lilly promises "competitive pricing" but has published no figure. Compounded GLP-1 medicines have been illegal to make or supply since 1 October 2024, and in March 2026 the TGA reported that imported unregistered products labelled as GLP-1 contained none.

On weight loss the evidence is not close: 20.9% for tirzepatide 15 mg against 3.1% on placebo, 5.4% for Contrave against 1.3%, and the 2026 BMJ network meta-analysis estimated the largest one-year weight loss of 19 drugs for tirzepatide and did not find naltrexone and bupropion convincingly different from lifestyle change. Contrave also had more people stop for side effects in its trials (23.8%) and has the longer list of people who cannot take it. What Contrave has is a price $140 to $440 a month below Mounjaro, a tablet instead of an injection, and none of the GLP-1 class risks. The Australian Journal of General Practice's 2025 review places incretin medicines such as Mounjaro first line for people with type 2 diabetes, cardiovascular disease, sleep apnoea or fatty liver disease, and naltrexone and bupropion as a reasonable option for people without cardiovascular disease or hypertension.

No Australian guideline covers moving from Contrave to Mounjaro or back, and neither Product Information mentions the other medicine or its class. The Contrave document contraindicates only other bupropion or naltrexone products, opioids and MAO inhibitors; the Mounjaro document says nothing about other weight-management medicines. The Wegovy and Saxenda documents, by contrast, say those products should not be used with other weight-management medicines because the combination has not been studied.

Taking them together has not been tested in a randomised trial, and no published study of the combination stands. The only one, a retrospective review from a single Vancouver clinic of naltrexone and bupropion added to semaglutide or liraglutide (International Journal of Obesity, 2024), was retracted by the journal on 19 December 2025 after concerns were raised about its statistical analysis; it did not involve tirzepatide and was never evidence of safety. An Australian Prescriber review in 2022 said liraglutide or semaglutide "could be combined" with naltrexone and bupropion; that is the author's opinion, and the author declared advisory roles with the makers of both. No Australian source gives a protocol.

A switch in either direction means starting the new medicine at its own starting dose and stepping up on its own schedule: Contrave over four weeks to four tablets a day, Mounjaro from 2.5 mg with 2.5 mg increases no sooner than every four weeks.

Weight regain after stopping is documented for tirzepatide: in SURMOUNT-4, people switched from tirzepatide to placebo regained 14% of their body weight over 52 weeks while those who continued lost a further 5.5%. The Contrave trials did not follow people after stopping, so no equivalent figure exists. Australian Prescriber's December 2025 review says that when treatment is stopped, regaining weight is the norm.