Lifestyle

Medications for Weight Management

5 min

❍ At a glance

  • Weight management medications work alongside dietary and behavioural support, not instead of it. Stopping medication typically leads to partial or complete weight regain. Semaglutide 2.4 mg weekly (Wegovy/STEP 1 trial) produces average 14.9% body weight loss - the largest effect size of currently available medications.5 Not PHARMAC-funded for weight management as of 2025.
  • PHARMAC-funded option: orlistat 120 mg (with criteria). Liraglutide 3 mg (Saxenda) and Wegovy are available on prescription but unfunded and expensive. Ozempic (semaglutide 0.5-2 mg) is funded for type 2 diabetes - off-label prescribing for weight loss without a diabetes indication has supply equity implications for people who need it for diabetes.
  • Prescribe with criteria in mind: BMI 30+ or BMI 27+ with weight-related comorbidity (T2DM, hypertension, OSA, significant joint disease), after meaningful lifestyle modification attempts. BMI has real limitations - consider clinical picture, not just the number.
  • GLP-1 agonists (liraglutide, semaglutide): nausea during dose escalation is nearly universal but typically settles. Contraindicated with personal or family history of medullary thyroid carcinoma or MEN2. Assess response at 12-16 weeks - if less than 5% weight loss at full dose, discontinue and discuss alternatives.

❍ Medications available in NZ

Orlistat (Xenical, 120 mg): blocks pancreatic lipase; roughly one-third of dietary fat passes unabsorbed. Average additional weight loss approximately 2.9 kg vs placebo over one year.2 Main side effects are gastrointestinal (oily stools, urgency, flatulence - worse with high-fat meals; can have useful behavioural effect). Fat-soluble vitamin supplementation at a different time recommended. PHARMAC-funded with criteria; also available OTC at 60 mg (Alli) - less effective.

Liraglutide (Saxenda, 3 mg daily): GLP-1 receptor agonist; slows gastric emptying, increases satiety. SCALE trial: 8.4% body weight loss vs 2.8% placebo over 56 weeks.4 Nausea common early (improves with gradual titration). Not PHARMAC-funded for weight management in NZ - requires private prescription. Contraindicated with MEN2 or medullary thyroid carcinoma history.

Semaglutide (Ozempic/Wegovy): GLP-1 receptor agonist, once weekly. STEP 1 trial (Wegovy 2.4 mg weekly): 14.9% body weight loss vs 2.4% placebo over 68 weeks.5 Similar side effect profile to liraglutide. Ozempic is PHARMAC-funded for T2DM with criteria; Wegovy for obesity management is not funded and had limited availability in NZ due to global supply constraints as of 2025. Avoid off-label Ozempic prescribing for weight loss without diabetes indication given supply equity implications.

Tirzepatide (Mounjaro): dual GIP/GLP-1 receptor agonist. SURMOUNT trial: approximately 20-22% body weight loss with highest doses.7 Approved in NZ for T2DM as of 2025; not funded or widely available for weight management. Landscape is evolving rapidly.

Phentermine: sympathomimetic stimulant; suppresses appetite via noradrenaline. Modest short-term weight loss (3-5 kg vs placebo over 12 weeks).6 Loses effectiveness over time. Schedule 4 controlled substance in NZ; typically short-term use only. Not suitable for cardiovascular disease, uncontrolled hypertension, or stimulant misuse history. Less commonly used as first-line given limitations.

📋 Patient handout - Weight management medications in NZ

❍ Prescribing considerations and monitoring

Stopping any weight management medication typically leads to weight regain - studies following semaglutide cessation after 68 weeks found most regained weight within a year.8 Frame this clearly in the initial consultation. Assess response at 12-16 weeks at full dose: less than 5% weight loss suggests the medication is not working for this patient - discontinue and discuss alternatives.

Monitoring: blood pressure and pulse with phentermine; review liver function considerations with orlistat where indicated; general response and tolerability review for all. Full medication review before prescribing - interactions and contraindications vary. Equity consideration: the most effective medications are unfunded in NZ, creating access barriers for many patients. If cost is prohibitive, document this and focus on funded options plus dietitian referral.

References

  1. MacLean PS, Bergouignan A, Cornier MA, Jackman MR. Biology's response to dieting: the impetus for weight regain. Am J Physiol Regul Integr Comp Physiol. 2011;301(3):R581-600.
  2. Rucker D, Padwal R, Li SK, Curioni C, Lau DC. Long term pharmacotherapy for obesity and overweight: updated meta-analysis. BMJ. 2007;335(7631):1194-9.
  3. Torgerson JS, Hauptman J, Boldrin MN, Sjostrom L. XENical in the prevention of diabetes in obese subjects (XENDOS) study. Diabetes Care. 2004;27(1):155-61.
  4. Pi-Sunyer X, Astrup A, Fujioka K, et al. A randomized, controlled trial of 3.0 mg of liraglutide in weight management. N Engl J Med. 2015;373(1):11-22.
  5. Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity. N Engl J Med. 2021;384(11):989-1002.
  6. Haddock CK, Poston WS, Dill PL, et al. Pharmacotherapy for obesity: a quantitative analysis of four decades of published randomized clinical trials. Int J Obes Relat Metab Disord. 2002;26(2):262-73.
  7. Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022;387(3):205-16.
  8. Wilding JPH, Batterham RL, Davies M, et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide. Diabetes Obes Metab. 2022;24(8):1553-64.