Introduction
Obesity is recognised as a chronic disease associated with increased risks of type 2 diabetes, cardiovascular disease, sleep apnoea, and certain cancers. Pharmacological therapy is considered alongside lifestyle changes for individuals with a BMI ≥30, or ≥27 with comorbidities.
Approved medications include:
GLP-1 Receptor Agonist
- Semaglutide (Wegovy/Ozempic, 2.4 mg/week):
- Functions by mimicking hormonal signals to reduce appetite and slow digestion.
- Average reported weight loss is approximately 15% over 68 weeks.
- Frequently observed side effects include nausea, vomiting, and diarrhoea; less commonly, gallbladder disorders, pancreatitis, and thyroid tumours may occur.
GIP/GLP-1 Receptor Agonist (Not currently available in New Zealand)
Tirzepatide:
- Is a dual GIP/GLP-1 receptor agonist, approved in 2023 for long-term weight management.
- Reported average weight loss is around 21% over 72 weeks, which is the highest among currently available pharmacotherapies.
- Primary adverse effects are gastrointestinal; there is also a noted risk of pancreatitis and gallbladder disease.
Centrally Acting Agents
Naltrexone/Bupropion ER (Contrave, oral):
- Acts on central nervous system pathways to reduce food cravings.
- Weight loss is typically 5–6% at one year.
- Adverse effects can include nausea, headache, insomnia, constipation, dry mouth, and increases in blood pressure and heart rate. The medication is contraindicated in individuals with uncontrolled hypertension, seizure disorders, opioid use, or those undergoing acute withdrawal from alcohol or sedatives.
Gastrointestinal Lipase Inhibitor
Orlistat (Xenical, 120 mg TDS):
- Reduces fat absorption by about 30%.
- Associated with an approximate 3% higher weight loss compared to placebo after one year.
- Side effects may include oily stools, faecal urgency, and flatulence. It may reduce absorption of fat-soluble vitamins, so supplementation is recommended. Orlistat is approved for long-term use, including in adolescents.
Summary
Pharmacological treatments for obesity in New Zealand include GLP-1 agonists (such as Wegovy/Ozempic,), demonstrate significant effects on weight and cardiometabolic parameters. Naltrexone/bupropion provides an oral option, though its use may be limited by tolerance issues and contraindications. Orlistat also remains available as a moderate efficacy alternative.
Selection of medication is based on factors such as patient comorbidities, cost and accessibility, contraindications, and individual treatment objectives. Weight-loss medications are usually prescribed in combination with lifestyle modification and are often intended for long-term administration, as discontinuation is frequently associated with weight regain.
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