How do weight-loss drugs like Mounjaro and Wegovy work?

Mounjaro and Wegovy have become the most talked-about medications in weight loss, with both now available through the NHS for eligible patients and widely accessible through private prescriptions. Both drugs belong to the GLP-1 receptor agonist class, which mimics glucagon-like peptide-1, a hormone that regulates appetite and blood sugar levels.

Wegovy, made by Novo Nordisk, was the first to gain mainstream attention. The drug works by slowing gastric emptying, meaning food stays in the stomach longer, triggering prolonged feelings of fullness. This reduces hunger signals to the brain, cutting overall calorie intake without requiring strict dietary discipline. Users typically inject weekly doses subcutaneously.

Mounjaro, produced by Eli Lilly, operates similarly but with a twist. It activates two hormone receptors instead of one: GLP-1 and GIP (glucose-dependent insulinotropic polypeptide). This dual-receptor approach creates a more potent appetite-suppressing effect. Clinical trials show Mounjaro users lose slightly more weight than Wegovy patients, though both deliver substantial results. Mounjaro also improves insulin sensitivity and blood sugar control, making it valuable for diabetic patients.

The NHS restricted access to both drugs initially, limiting prescriptions to patients with a BMI over 35 or 30 with weight-related health conditions. Recent policy shifts have expanded eligibility. Weight loss typically ranges from 15 to 22 percent of body weight over six months to a year.

Common side effects include nausea, vomiting, and gastrointestinal discomfort, usually temporary during the adjustment phase. Both require ongoing injections. Stopping either medication causes weight regain in most users, making these treatments maintenance drugs rather than cures.

The surge in demand has strained supply chains globally. Novo Nordisk and Eli Lilly struggle to meet prescription requests, particularly in the US. Celebrities and influencers openly using these drugs have driven off-label demand, further straining availability for med