Antiobesity agents can only help overweight patients lose weight when used in conjunction with a restricted-energy diet. They should only be used to treat patients with severe obesity, i.e. body mass index (BMI) ≥30 kg/m2 or BMI ≥28 kg/m2 with associated risk factors. Patients should receive advice on diet and lifestyle modification and be monitored for changes in weight, blood pressure and lipids.
Bulking agents are taken with water before meals. They swell in the stomach and help overcome the feeling of emptiness. Prolonged use of bulking agents may lead to tolerance and may not help bring about the behaviour changes that the obese patient needs to make.
The lipase inhibitor orlistat is a long acting inhibitor of gastrointestinal lipases. It acts within the stomach and small intestine preventing the hydrolysis and subsequent absorption of up to one third of ingested dietary fat.
The GLP-1 agonist liraglutide acts mainly to reduce fat mass; it regulates appetite by increasing feelings of fullness and lowering feelings of hunger.
The combination of naltrexone and bupropion is thought to have synergistic actions on the appetite-regulating melanocortin system and the dopaminergic reward pathways in the CNS.