Looking for a semaglutide substitute? Here's what the evidence says

Which medicines can actually substitute for semaglutide in weight management?

In the UK, the licensed options for weight management are narrow by design. Semaglutide, sold as Wegovy by Novo Nordisk, is a once-weekly injection. Tirzepatide, sold as Mounjaro by Eli Lilly, is the other major option, also a once-weekly injection. Both require a prescription following clinical assessment, and both carry a Black Triangle (▼) marker, meaning the MHRA collects additional safety data on them. You can read the clinical detail on how Wegovy works and on semaglutide's licensed uses separately.

Orlistat is an older oral medicine that blocks fat absorption rather than acting on appetite hormones. It is considerably less effective than either GLP-1 class drug in trials, but it remains licensed and can suit people for whom injections are unsuitable or who have specific clinical reasons to avoid GLP-1 medicines. It is not a like-for-like substitute for semaglutide, but it is a legitimate alternative in certain situations.

Compounded or unlicensed semaglutide (sometimes sold online, sometimes described as reconstituted powder) is a separate matter entirely and is covered below. The short answer is that it is not the same as a licensed medicine and carries real risks.

Lifestyle change alongside diet and increased activity remains the foundation of any weight management plan, whatever medicine is or isn't involved. The weight-loss treatment overview sets out how medicines fit into that broader picture.

How does tirzepatide actually differ from semaglutide as a substitute?

This is the question that matters most if you're considering a switch. Semaglutide works by mimicking GLP-1, a gut hormone that signals fullness and slows gastric emptying. Tirzepatide does the same thing, but it also activates GIP receptors, a second gut hormone pathway involved in appetite and blood sugar. That dual action is why the two medicines are not simply interchangeable copies of one another.

The clinical evidence for tirzepatide as a substitute is strong. NICE's appraisal of tirzepatide (published as TA1026) noted that indirect comparisons favour tirzepatide, and the SURMOUNT-5 trial published in the New England Journal of Medicine (2025) put that to a direct test: tirzepatide produced a greater average weight reduction than semaglutide 2.4mg over 72 weeks in adults with obesity who did not have diabetes. That is currently the best head-to-head evidence available.

At the same time, semaglutide has a longer track record in clinical practice, more published safety data, and suits some people better than tirzepatide, particularly those who have already tolerated it well. A larger maintenance dose of semaglutide, the 7.2mg pen approved by the MHRA in early 2026, narrows the results gap with high-dose tirzepatide. Which option is appropriate for a given person is a clinical judgement, not a straightforward upgrade.

If you're curious about the cost side of the comparison, the cost of Wegovy in the UK page gives honest market context.

What about reconstituted semaglutide, is that a legitimate substitute?

This comes up often and deserves a direct answer. Reconstituted semaglutide refers to a powder form of semaglutide that must be mixed with a solution before injection. It is not a licensed medicine in the UK and is not the same product as Wegovy. The MHRA has issued repeated public warnings about unlicensed weight-loss injectables sold online, including counterfeit pens and unregulated compounded products. Some of what's been seized has contained incorrect doses or entirely different substances.

Pages on reconstituting semaglutide and the reconstitution process cover what's involved, but those are educational resources, not an endorsement of unlicensed products. The NHS semaglutide page is the clearest starting point for understanding what the licensed medicine looks like and how it differs from alternatives that circulate outside the regulated supply chain.

A licensed medicine sourced through a GPhC-registered pharmacy means a prescription has been issued by a qualified prescriber, the product has passed MHRA standards, and the supply chain is traceable. That is the meaningful baseline for any substitute, not the price.

When does it make sense to consider switching, and how does that work?

People look for a semaglutide substitute for different reasons: supply issues, side effects that haven't settled, insufficient weight loss after reaching the maintenance dose, or a change in their health picture that makes a different medicine more appropriate. NICE guidance notes that if weight loss is less than 5% after six months at the highest tolerated dose, continuing treatment should be reviewed, and that review might include whether a different medicine is worth trying.

Switching is not a self-referral process. A prescriber will want to know how long you've been on the current medicine, what dose you reached, what side effects occurred, what your weight trajectory looks like, and whether any other conditions have changed. Transfer patients at nume (sorry, at our pharmacy) are asked for evidence of current treatment before any new prescription is issued. That isn't bureaucracy; it's the clinical minimum needed to prescribe safely.

The Wegovy substitutes page looks at the switching question from a slightly different angle if you're already on Wegovy specifically and wondering what else exists. And if you're at the stage of wanting a prescriber to look at your situation properly, a free consultation is the place to start.