Orlistat vs Wegovy: which weight-loss medicine makes more sense for you?

How do orlistat and Wegovy actually work, and why does that difference matter?

Orlistat is a lipase inhibitor. Swallowed with meals, it prevents roughly a third of the fat you eat from being absorbed, so those calories pass through rather than entering your bloodstream. The effect is local and mechanical. It does not touch hunger, appetite hormones or the brain's reward response to food. If you eat a low-fat meal, the medicine has very little to act on.

Wegovy is a once-weekly injection of semaglutide, a GLP-1 receptor agonist. It mimics a gut hormone that signals fullness to the brain, slows gastric emptying and dampens appetite through a central pathway. The effect is systemic: most people eating on Wegovy find they feel satisfied faster and think about food less, regardless of what's on the plate.

That distinction shapes almost everything downstream, results, side effects, how you take it and who it suits. The NHS medicines page for semaglutide gives a clear overview of how the GLP-1 mechanism is thought to work in practice. The NHS orlistat page is equally readable if you want the detail on the fat-blocking pathway. Worth reading both before the comparison table below starts to make real sense.

What do the clinical trial results actually show for each medicine?

The headline numbers are not close. In the STEP 1 trial (68 weeks, semaglutide 2.4mg versus placebo, roughly 1,900 adults) participants lost an average of around 15% of their body weight. That is a figure cited directly by NICE's appraisal of Wegovy (TA875) as the basis for its recommendation. For context, someone weighing 100 kg would be looking at an average reduction of about 15 kg over 68 weeks.

Orlistat produces more modest results. In trials, the addition of orlistat to a calorie-reduced diet produced roughly 3–5% greater weight loss than diet alone over one year. If you want to dig into how orlistat and semaglutide compare across the clinical evidence, we cover the detail on that dedicated page. That is a meaningful effect, but it belongs to a different order of magnitude from injectable GLP-1 treatment.

The table below summarises the key differences factually.

Neither medicine replaces dietary changes and physical activity. Both licences make that clear.

Who is each medicine licensed for, and do the eligibility criteria differ?

Wegovy's licensed population in the UK covers adults with a BMI of 30 or above, or 27 to 29.9 with at least one weight-related condition such as high blood pressure, type 2 diabetes or high cholesterol. Lower BMI thresholds apply for some ethnic backgrounds under UK clinical guidance. Prescription-strength orlistat carries a similar BMI threshold, though the clinical picture that makes it appropriate differs: it suits people whose diet is already relatively high in fat and who can practically manage the GI side effects around daily life.

NICE's Wegovy recommendation (TA875) adds an extra layer for NHS access: treatment should be within a specialist multidisciplinary weight management service, for a maximum of two years, with the option to continue reviewed at six months if weight loss falls below 5% on the maintenance dose. Private prescribing follows the licensed criteria rather than NHS commissioning restrictions, which is where a service like nume's clinical model fits in, though every consultation is still an individual clinical assessment, not a tick-box exercise.

Neither medicine is suitable during pregnancy, while breastfeeding, or if you are actively trying to conceive. Under-18s are not a licensed population for either treatment. A prescriber needs the full picture before deciding which, if either, is appropriate for you.

Is one of them available on the NHS more easily than the other?

In practice, NHS access to Wegovy is limited by the specialist-service requirement under TA875; waiting lists in many areas are substantial. Orlistat has been available on NHS prescription for longer and can be prescribed in primary care, making it more accessible through a GP for those who meet the clinical criteria. That does not make orlistat the better choice, it reflects commissioning history more than clinical ranking.

For Wegovy specifically, the private route is the realistic option for most people who want to start now. A legitimate private prescription still requires a clinical assessment from a registered prescriber; the absence of a waiting list does not remove that step. You can explore the full Wegovy overview for more on what private treatment involves, or read about how Wegovy and Ozempic differ if you are unsure which semaglutide product applies to your situation. If you are weighing up Wegovy against other options, our Wegovy comparisons page sets out how it stacks up across a range of alternatives. If orlistat or another pathway suits your situation better, that is the conversation to have at the consultation stage. Which medicine makes sense for you is a clinical decision our prescribers make with you, not something a comparison page can settle.

If you're ready to take that step, check your eligibility with a free consultation.