Obesity

Medications for Weight Management

• Phentermine (sympathomimetic)

  • Mechanism: Appetite suppression

  • Avoid in patients with cardiovascular disease, uncontrolled hypertension, anxiety, or substance misuse

  • TGA-approved for short-term use (≤12 weeks)

• Orlistat

  • Mechanism: Inhibits pancreatic lipase, reducing fat absorption

  • Side effects: Steatorrhoea, flatulence, potential deficiency of fat-soluble vitamins (A, D, E, K)

• Liraglutide / Semaglutide (GLP-1 Receptor Agonists)

  • Mechanism: Slows gastric emptying, promotes satiety

  • Preferred in patients with T2DM or high cardiovascular risk

  • Monitor for gastrointestinal side effects (nausea, vomiting)

• Naltrexone / Bupropion

  • Mechanism: Central appetite suppression and reward pathway modulation

  • Avoid in epilepsy, severe uncontrolled hypertension, or patients at high risk of seizures

  • Caution: May raise blood pressure and heart rate

• Notes

  • VLED (Very Low Energy Diet) can be used with similar BMI thresholds (≥30, or ≥27 with obesity-related comorbidities), but take care in those using insulin, sulfonylureas, or SGLT2 inhibitors (increased risk of hypoglycaemia or euglycaemic DKA)

  • Avoid all anti-obesity medications in pregnancy (liraglutide not specifically TGA-indicated in pregnancy)

  • Topiramate has off-label weight loss effects but is not TGA-approved for obesity management and has ocular side effects (risk of acute angle-closure glaucoma)

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Indications for Starting Medications

• BMI ≥30 kg/m², or ≥27 kg/m² with obesity-related complications (e.g. T2DM, hypertension, NAFLD, OSA)

• Must be combined with lifestyle interventions (diet, physical activity, behavioural support)

• Continue only if clinically meaningful weight loss (≥5% from baseline) is achieved within 12 weeks

• Regularly review safety profile and ongoing adherence

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Consider Surgery (Sleeve Gastrectomy or Other Bariatric Procedures)

• In diabetic patients with BMI >40 or BMI >35 plus ≥1 obesity-related complication, especially if glycaemic control is difficult to achieve

• Surgical approach can result in significant and sustained weight reduction, remission or improvement in T2DM, and reduced cardiovascular risk

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Referral Criteria for Bariatric Surgery

• BMI >35 kg/m² regardless of comorbidities

• BMI >30 kg/m² with obesity-related comorbidities (e.g. T2DM, OSA, uncontrolled hypertension)

• Conditions requiring specialist management (severe OSA, complex T2DM)

• Psychological readiness and commitment to long-term follow-up

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Non-Pharmacological Management

• Dietary Approaches

  • Tailor to patient preferences (Mediterranean, low-carb, meal replacements)

  • Energy deficit of ~500–750 kcal/day for gradual, sustainable weight loss

  • Monitor calcium and protein intake if using VLED or meal replacements

• Physical Activity

  • At least 150–300 minutes per week of moderate-to-vigorous activity

  • Include resistance training 2–3 times per week for muscle preservation

  • Even without major weight loss, exercise reduces ASCVD risk and improves metabolic health

• Behavioural Support

  • SMART goal-setting, self-monitoring of weight and dietary intake

  • Cognitive behavioural strategies to prevent relapse (stress management, problem-solving)

  • Regular follow-up and accountability (group programs, online tools)

• Lifestyle Targets

  • Aim for ≥5–10% weight reduction over 6–12 months

  • Address psychosocial factors (sleep hygiene, mental health, readiness for change)

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Notes:

• Obesity-related complications include T2DM, hypertension, IHD, OSA, NAFLD, PCOS, and arthritis

• Bariatric surgery considered at lower BMI thresholds (≥30) if severe comorbidities exist (e.g. difficult-to-control diabetes)

• In pregnancy planning, discontinue weight loss medications except under specialist guidance (risks vs benefits)

• Regular reviews are important to reassess treatment efficacy, potential adverse effects, and patient adherence

• Implement a comprehensive approach: diet, exercise, behavioural therapy, plus medication or surgery if indicated

• Use motivational interviewing and shared decision-making to support lifestyle changes

• Monitor for medication side effects (e.g. orlistat’s GI effects, phentermine’s cardiovascular effects)

• Refer patients with significant comorbidities or inadequate response to lifestyle interventions for specialist evaluation, including bariatric surgery assessment

• Long-term follow-up is vital for maintaining weight loss and optimising metabolic health