Alli vs Wegovy: comparing two very different approaches to weight loss

You're standing in the pharmacy aisle wondering whether a prescription is really necessary

Alli is the only weight-loss medicine in the UK you can buy without a prescription. It contains orlistat 60 mg (half the prescription dose) and works in the gut, not the brain: it inhibits pancreatic lipase, which means roughly a third of dietary fat passes through undigested rather than being absorbed. The appeal is obvious: no GP appointment, no waiting room, available from any pharmacy or online retailer. The trade-off is meaningful. Clinical trial data for orlistat at the 60 mg dose show modest average weight loss, typically around 3 to 5 per cent of body weight over six months in participants who also followed a low-fat diet. Side effects from unabsorbed fat are real: oily stools, urgent bowel movements and flatulence are common, particularly if fat intake isn't controlled. The NHS medicines page on orlistat sets this out plainly and is worth reading before you start. Alli suits people who want a non-prescription option, are committed to a low-fat eating pattern, and have realistic expectations about the scale of results.

Wegovy is a prescription-only medicine (POM) in the UK. You cannot and should not be able to obtain it without clinical assessment. That isn't a bureaucratic inconvenience, it reflects a genuinely different risk and benefit profile. If you want to understand exactly how those two medicines differ before reading further, our page covering Wegovy vs Ozempic also explains what makes Wegovy distinct as a licensed weight-loss treatment, which gives useful context for the comparison with Alli.

What the trial evidence says, side by side

A question our prescribers hear most weeks is whether Wegovy's results are really that different from orlistat's, or whether the extra step of a prescription is worth it. The trial data are unambiguous on the gap. The STEP 1 trial (published in the New England Journal of Medicine) followed 1,961 adults with obesity over 68 weeks using semaglutide 2.4 mg alongside lifestyle support. Average weight loss was around 15 per cent of body weight. In absolute terms, that is a substantially different outcome from the 3–5 per cent seen with orlistat 60 mg. NICE's appraisal of semaglutide (TA875) accepted this evidence base and recommended it for NHS use within specialist weight-management services.

No head-to-head randomised trial has directly compared orlistat 60 mg with semaglutide 2.4 mg. The figures above come from separate studies with different populations and designs, so treat the comparison as directional rather than precise. That said, the direction is consistent across the evidence.

Who can actually access each option, and what the eligibility looks like in practice

Alli is licensed for adults aged 18 and over with a BMI of 28 or above. No formal clinical review is required at the point of purchase, though the pack includes guidance on a fat-reduced diet and asks you to read the leaflet carefully. You buy it, you start it.

Wegovy's licensed eligibility in the UK sits at BMI 30 or above, or BMI 27 or above alongside 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 guidance. Crucially, meeting the BMI number alone doesn't guarantee a prescription: a prescriber considers your full medical history, any medicines you take, and contraindications such as a personal or family history of medullary thyroid cancer. Pregnancy, breastfeeding, and trying to conceive are all situations where Wegovy isn't recommended. The broader GLP-1 landscape helps explain why eligibility requirements differ so much across this class of medicines.

On the NHS, Wegovy is available through specialist weight-management services under NICE TA875, waiting lists can be long. Through a regulated private pharmacy like nume, there is no waiting list, and the same clinical assessment applies: a prescriber still reviews your consultation before anything is dispensed.

Everyday life on each treatment, and what drives the choice

Living with Alli means watching fat intake closely. Meals that are too high in fat trigger GI side effects that can be disruptive and embarrassing. Many people find this enforces dietary change by a mechanism they hadn't bargained for. The capsules are taken up to three times a day with meals, which suits some people and not others.

Wegovy involves a once-weekly injection, which sounds daunting but most patients adapt to quickly. The nausea that can follow the first few weeks is the most common reason people contact our team, it is real, but it tends to ease as the body adjusts, and it rarely lasts as long as people fear. The new oral semaglutide tablet (approved by the MHRA in June 2026) offers a needle-free alternative for those on the Wegovy pathway who prefer it. You can read more about how different semaglutide formulations compare if that's relevant to your situation.

For a fuller picture of how Wegovy sits alongside other medicines in this space (including where Saxenda, Mounjaro and others fit) our Wegovy comparisons hub pulls it together. If you're already exploring the prescription pathway, our free consultation is the right next step: a prescriber reviews your details the same day and will tell you clearly which option, if any, is appropriate for you. That clinical decision is one we make with you, not for you.