Medication and surgery for adults
Treatment guidelines recommend consideration of additional therapies such as pharmacotherapy and bariatric surgery when lifestyle intervention has not resulted in sufficient weight loss to improve health or quality of life. This page summarises the evidence for the use of medications, gastrointestinal devices and bariatric surgery to treat adults with overweight and obesity.
Key Evidence
Pharmacotherapy is indicated in addition to lifestyle intervention in people with overweight and weight-related health problems, or people with obesity
Six medications are approved by the Therapeutic Goods Administration (TGA) for the treatment of obesity in Australia
Bariatric surgery is the most efficacious long-term treatment for obesity and should be considered along with individual circumstances
Combinations of treatment options may be needed to achieve treatment goals
Overweight and obesity have complex biological, psychosocial and environmental determinants, and are not simply the result of an unhealthy lifestyle.12 Lifestyle intervention, including changes in eating habits and physical activity, is the foundation of obesity management. However, lifestyle interventions alone are often ineffective in achieving sustained weight loss.2 This is in part due to the physiological changes and metabolic adaptation that occurs with weight loss and the ongoing influence of factors that contributed to weight gain in the first place, such as appetite regulation.23 It is therefore not surprising that obesity, like other chronic conditions, is not ‘cured’ by the initial phase of treatment (in this case, weight loss), and requires long-term, multidisciplinary management to address the drivers of obesity.
Treatment guidelines recommend consideration of additional therapies such as pharmacotherapy and bariatric surgery when lifestyle intervention alone has not achieved sufficient weight loss to improve health or quality of life.45678
Medications
A range of medications are available for weight management treatment, to be used in combination with lifestyle interventions.2910 Obesity pharmacotherapy is indicated as a treatment option for people with a BMI ≥ 27 kg/m2 and with a weight-related health problem, or people with obesity (BMI > 30 kg/m2).10 Pharmacotherapy may be useful in inducing weight loss, or preventing weight regain. Six medications are approved by the Therapeutic Goods Administration (TGA) for the treatment of obesity in Australia (Table 1) – phentermine, orlistat, liraglutide, semaglutide, tirzepatide, and naltrexone-bupropion.8 With the exception of orlistat, which reduces absorption of ingested calories, the medications used to treat obesity primarily act via effects on appetite (reducing hunger and/or increasing satiation).10
Semaglutide (brand name Wegovy®) is a glucagon-like peptide 1 (GLP1) receptor agonist that is administered as a subcutaneous injection once a week.11 It is currently approved in Australia for use in obesity management (Wegovy®) and results in mean weight loss in people without diabetes of 14.7-17.4% at 68 weeks, and 15.2% at 2 years.2101213 The STEP trials found semaglutide had beneficial effects on health markers such as blood pressure, glycaemia, lipids, inflammation and anthropometric parameters.1314 Side effects are predominately gastrointestinal such as nausea, constipation and diarrhoea. 2101314
Tirzepatide (brand name Mounjaro®) is also administered by subcutaneous injection once a week and is a glucose-dependent insulinotropic polypeptide (GIP) and GLP-1 receptor agonist.14 Tirzepatide (Mounjaro®) is approved in Australia for obesity management. The SURMOUNT trials found tirzepatide results in weight loss of 15% (5mg dose) to 20.9% (15mg dose) at 72 weeks, and 25.3% (10-15mg dose) at 88 weeks.15 It reduces energy intake by reducing appetite.16 Tirzepatide improves cardiometabolic measures including blood pressure, fasting insulin level, lipid levels and waist circumference.15 As with semaglutide, side effects include gastrointestinal symptoms such as nausea, diarrhea and constipation.15
In December 2025, Saxenda® (liraglutide) will be discontinued in Australia. The manufacturers report making the decision based on Wegovy® being more effective for weight loss.1718 The choice of medication is dependent on individual factors and preferences. Clinical trials indicate that on average, the most effective weight loss drugs are the newest generation of weight management medication, tirzepatide (17.8% mean placebo-subtracted weight loss at 72 weeks)15 and semaglutide (12·5% mean placebo-subtracted weight loss at 68 weeks)212 Liraglutide, orlistat, phentermine and naltrexone plus bupropion have been found to have similar weight loss efficacy in clinical trials of around 4-6% over 12 months (Table 1).19 A trial published in 2025 comparing tirzepatide and semaglutide found greater mean weight loss from tirzepatide of 20.2% at 72 weeks compared to 13.7% with semaglutide and also resulted in greater reductions in waist circumference of 18.4cm and 13.0cm, respectively.20
There is considerable variation between individuals in treatment response. In an analysis of randomised clinical trials of people with and without T2D who used liraglutide, naltrexone-bupropion and orlistat at the recommended doses for ≥1 year, weight loss of 5% or more was achieved by 63, 55 and 44% of participants, respectively, compared with 23% of placebo participants, and ≥10% weight loss occurred in 34, 30 and 20% of participants after 12 months’ use compared to 9% with placebo.21 It should be noted that some of the studies included in this analysis used very intensive lifestyle interventions, and weight outcomes in both placebo and active intervention groups are often better in clinical trials compared with real-world results.
Weight loss of 5% is sufficient to bring about improvements in some weight-related complications see Health benefits of weight loss. All of the available medications are associated with improvements in cardiometabolic risk profile, although each medication has favourable effects on different risk factors.2022
Data on long-term safety and effectiveness of obesity medication for weight management are limited.20 Similar to treating other chronic diseases with medication, it is expected that treatment will be required over the long-term, as the medications are only effective while in use.20 The cessation of obesity medication commonly leads to weight regain.162324 A study on the long-term effectiveness of semaglutide showed weight loss is maintained at 4 years (mean weight loss 10.2%, mean reduction in waist circumference 7.7 cm) and was associated with fewer major adverse cardiovascular events compared to placebo.25 Regular follow up is important to monitor and establish effectiveness, tolerability, adverse effects and adherence.10
Equitable access to obesity medications is lacking, as none are currently subsidised under the Pharmaceutical Benefits Scheme (PBS) for weight management. However, check the PBS website for updates. Additionally, this area is rapidly evolving so it is recommended to check the TGA for the latest updates on medications approved for weight management.
Table 1: Medications approved for the treatment of obesity in Australia
Table adapted from Markovic (2022) and Draft Clinical Practice Guidelines for the Management of Overweight and Obesity for Adults, Adolescents and Children in Australia 2024 (based on Walmsley et al (2023) with information on Tirzepatide from Lingvay et al (2024) and Jastreboff et al (2022).
| Medication | Phentermine (Duromine® Metermine®) | Orlistat (Xenical®) | Liraglutide (Saxenda®) | Naltrexone-Bupropion (Contrave®) | Semaglutide (Wegovy®) | Tirzepatide (Mounjaro®) |
|---|---|---|---|---|---|---|
| Route and Form | Oral (capsule) | Oral (tablet) | Subcutaneous (injection) | Oral (tablet) | Subcutaneous (injection) | Subcutaneous (injection) |
| Mechanism of action for weight loss | Appetite reduction by stimulation of neural release of dopamine, noradrenaline, and serotonin | Reduces the absorption of dietary fat by inhibiting gastric and pancreatic lipases | Appetite reduction by stimulating GLP‐1 receptors in the brain | Appetite reduction by stimulating activity of POMC neurons in the hypothalamus | Appetite reduction by stimulating GLP‐1 receptors in the brain | Appetite reduction. Dual GIP/GLP-1 receptor agonism |
| TGA approved population for use | Adolescents and adults | Adolescents and adults | Adults only | Adults only | Adolescents and adults | Adults only |
| Mean placebo-subtracted weight loss in clinical trials | 7.4 kg over 36 weeks | 4% at 52 weeks | 4–6% at 56 weeks | 5% at 56 weeks | 12–14% at 68 weeks | 17.8% at 72 weeks |
| Proportion of participants with 5% and 10% weight loss at 12 months | Not reported | 73% and 41% (v 45% and 21% placebo) | 63% and 33% (v 27% and 11% placebo) | 48% and 25% (v 16% and 7% placebo) | 86% and 69% (v 32% and 12% placebo) | 91% and 84% (35 and 19% placebo |
| Contraindications and precautions | • Coronary artery disease | • Pregnancy | • Pregnancy | • Pregnancy | • Pregnancy | • Pregnancy |
| • Uncontrolled hypertension | • Breastfeeding | • Breastfeeding | • Breastfeeding | • Breastfeeding | • Personal or family history of medullary thyroid carcinoma or, | |
| • Hyperthyroidism | • Chronic malabsorption syndrome | • Personal or family history of medullary thyroid carcinoma or, | • Uncontrolled hypertension | • Personal or family history of medullary thyroid carcinoma or, | • Multiple endocrine neoplasia syndrome type 2 | |
| • Glaucoma | • Cholestasis | • Multiple endocrine neoplasia syndrome type 2 | • Seizure disorders | • Multiple endocrine neoplasia syndrome type | ||
| • Cardiac arrhythmias | • Bipolar disorder | |||||
| • MAOI | • Undergoing abrupt discontinuation of alcohol or anticonvulsant drugs | |||||
| • Pregnancy | • Chronic opioid use | |||||
| • Breastfeeding | • MAOI | |||||
| • Not recommended with SSRIs | ||||||
| Common side effects | • Dry mouth | • Steatorrhea | • Nausea | • Nausea | • Nausea | • Nausea |
| • Insomnia | • Oily spotting | • Diarrhoea | • Constipation | • Diarrhoea | • Diarrhoea | |
| • Palpitations | • Faecal urgency | • Constipation | • Headache | • Constipation | • Constipation | |
| • Tachycardia | • Fat-soluble vitamin deficiency | • Vomiting | • Vomiting | • Vomiting | • Vomiting | |
| • Hypertension | • Headache | • Dizziness | • Headache | • Headache | ||
| • Anxiety | • Dyspepsia | • Insomnia | • Dyspepsia | • Dyspepsia | ||
| • Dizziness | • Cholelithiasis | • Dry mouth | • Cholelithiasis | • Cholelithiasis | ||
| • Constipation | • Diarrhoea | |||||
| • Hypertension |
Over-the-counter weight loss supplements
There is a plethora of non-prescription weight loss supplements and herbal medicines available for sale in pharmacies and supermarkets in Australia, and sales suggest that they are widely consumed. They promise easy weight loss but there is no evidence that any of these products are of any value to assist weight loss, and some may be counterproductive or unsafe.26
Gastrointestinal devices and endoscopic procedures
Gastrointestinal devices and procedures, such as intragastric balloons and endoscopic sleeve gastrectomy, are inserted endoscopically. One of the first such procedures was the endoscopic intragastric balloon, also known as the gastric balloon. An intragastric balloon is an inflatable silicone balloon that is inserted in the stomach (with an endoscope that enters the gastrointestinal tract through the mouth) and facilitates weight loss by people feeling full sooner thereby reducing intake.27 It is designed for short-term use and requires removal after 6-12 months (depending on the type).27 After removal of the gastric balloon, weight regain is common.28 Weight loss can be greater than medication initially, but less than with surgical procedures.12829 For example a study found greater average weight loss at 6 months in participants who had an intragastric balloon (12.7kg) compared to those on semaglutide (9.4kg), however, there were no significant differences at 12 months.29 The swallowable gastric balloon (also known as the procedureless gastric balloon) is swallowed as a capsule and expanded once correctly placed in the stomach using a solution delivered through a catheter.30 The balloon automatically deflates after 4 months and is passed through the digestive system.30 A systematic review and meta-analysis found it is effective for short-term weight loss with average weight loss of 12.47% after 4 months.31
One of the newer procedures is the endoscopic sleeve gastroplasty in which stitches are placed inside the stomach to reduce its capacity.232 A randomised controlled trial found significantly greater weight loss achieved from endoscopic sleeve gastroplasty than lifestyle modification.33 The endoscopic sleeve gastroplasty is similarly minimally invasive, however achieves greater and longer lasting weight loss than the intragastric balloon with mean total weight loss at 12 months of 17.51% and 10.35% respectfully.32
These endoscopic procedures achieve greater weight loss than lifestyle modification, however, although infrequent, they do carry risks of adverse events.2832 The suitability of endoscopic procedures as a treatment option for an individual, should consider their circumstances, goals and treatment costs, given costs can approach that of bariatric surgery but has inferior long-term weight loss outcomes.
Bariatric surgery
Bariatric surgery should be considered as part of a comprehensive multidisciplinary treatment program taking into account the individual’s situation and treatment goals. International34 and draft national8 guidelines recommend consideration of bariatric surgery for:
- individuals with BMI ≥35 kg/m2, regardless of presence or severity of co-morbidities.
- individuals with BMI of 30–34.9 kg/m2 who do not achieve durable weight loss or co-morbidity improvement using nonsurgical methods.
Additionally, international guidelines34, including a position statement from Diabetes Australia35, recommend consideration of bariatric surgery for individuals with type 2 diabetes and BMI ≥30 kg/m2.
The most common bariatric procedure in Australia is the sleeve gastrectomy (SG), which made up 80% of bariatric surgeries in 2023.36 Gastric bypass, such as one anastomosis gastric bypass (OAGB) and Roux-en-Y gastric bypass (RYGB), were the next most common procedures at 11% and 9% respectively.36 The choice of procedure depends on the individual goals of treatment, available expertise (surgeon and institution), patient preferences and personalised risk stratification.37 There have been considerable improvements in the safety of bariatric surgery over recent decades, partly due to the increasing use of laparoscopic procedures.38
A randomised controlled trial compared patient outcomes at 5 years post SG and RYGB and found both effective but no statistically significant difference in weight loss.39 A systematic review and meta-analysis in 2022 compared outcomes of SG, RYGB and OAGB. The study found RYGB had the greatest weight loss at 3 years follow-up, however OAGB was greater than RYGB at 12 months.40
Bariatric surgery is the most efficacious long-term treatment for obesity, achieving weight losses of around 25-30% with SG and RYGB at 1 year.4142 As with all obesity treatments, there is considerable inter-individual variation in response: more than half of people who undergo RYGB will have weight loss of 25% or more at 1 year. Some weight regain (on average 5-10% at 10 years) is expected in the longer term.43
Bariatric surgery also results in marked improvements in most weight-related health conditions, particularly type 2 diabetes (T2D). In a meta-analysis of randomised controlled trials comparing surgery with medical treatment of T2D in 463 patients with follow-up of at least 2 years, diabetes remission was seen in 53% of bariatric surgery participants compared with 4% of participants who did not undergo surgery.44 In four studies with 5 years’ follow-up, diabetes remission was seen in 28% of surgical and 4% of medically-treated participants.44 Similarly positive findings for bariatric surgery on type 2 diabetes were found in a national registry of 122,567 patients between 2012-2021.45 Of the 13,904 who were treated for diabetes at baseline, 71.6% no longer required diabetes medication at 1 year, and 61% at 5 years.45 A meta-analysis of matched cohort and prospective controlled studies of 174,772 participants found bariatric surgery compared to usual care was associated with lower rates of all-cause mortality and longer life expectancy, with greater improvements for those with pre-existing diabetes.46
Available evidence from observational cohort studies indicates a lower risk of microvascular events (damage to eyes, kidneys and nerves) after bariatric surgery compared to non-surgical treatment in people with T2D after at least 5 years’ follow-up,47 and of cardiovascular events and overall mortality in people with and without diabetes.48 Surgical treatment of obesity is also associated with improvements in cardiometabolic risk factors and numerous other weight-related issues such as obstructive sleep apnoea,49 non-alcoholic fatty liver disease,50 cancer incidence,51 sexual function52 and quality of life, particularly physical wellbeing.53 A 2024 systematic review and meta-analysis found better long-term outcomes for weight loss and health markers from surgery than pharmacological treatments, noting both were effective.54 This comparison will require updating as evidence grows on the effectiveness of newer weight management medications.54
Bariatric surgery is generally safe and can substantially improve health, however there are potential side-effects. Numerous studies have reported low mortality rates, such as 0.1% in an Australian national registry of patients,45 and 0.03% to 0.2% in US studies.55 Defined adverse events (unplanned readmission, intensive care admission and re‐operation; death) at 90-days post-surgery are reported in 3.6% of procedures in Australia.45 Reduced gastric capacity may result in gastrointestinal side effects such as vomiting, reflux, and pain upon eating.56 Dumping syndrome, while rare and more common after bypass procedures, can be particularly problematic with symptoms including abdominal cramps, diarrhoea and hypoglycaemia. Excess skin following substantial weight loss can contribute to body dissatisfaction and physical discomfort.57 Long-term follow up is important to monitor and manage potential side effects such as nutrient deficiencies58 and bone density changes for osteoporosis risk.59 Although many people experience improvements in quality of life after bariatric surgery, some people experience the persistence or reappearance of psychological problems such as depression, excess alcohol consumption and other self-harming behaviours.606162
As with medical treatment of obesity, there is inequitable access to bariatric surgery in Australia, with far more procedures conducted in the private than public sector.63 The potential demand for bariatric surgery far outstrips supply – it was estimated that of the 3.35 million Australians with obesity aged 18 to 65 years in 2011-2013, more than one quarter were potentially eligible for bariatric surgery (accounting for 6% of the population aged 18–65 years).64 However, in 2018-2019 only 41,534 bariatric procedures were performed and just 7% of these were done in the public sector.63 A 2022 study modelled bariatric surgery eligibility compared to supply over a 5-year period, and found Australia would need a nine-fold increase in surgical capacity to meet demand, which would also lead to overall cost savings.63 A meta-analysis of 61 studies concluded that overall, bariatric surgery is cost saving over the life course, even without considering indirect costs, such as reduction in medication usage.65 The 2023 Annual Report from the Australia and New Zealand Bariatric Surgery Registry found rates of bariatric surgery have decreased, potentially in part due to improvements in pharmacological treatments, and cost of living pressures.36
Combination therapies
Similar to most chronic diseases, a combination of treatments may be required to achieve a patient’s treatment goals.256 For example, the use of pharmacological therapy following bariatric surgery, or the use of medication to achieve weight loss goals before bariatric surgery.25
Content for this page was updated by Josephine Marshall, Deakin University, and reviewed by Dr Priya Sumithran and Associate Professor Tania Markovic. For more information about the approach to content on the site please see About | Obesity Evidence Hub.