Semaglutide or Tirzepatide: How Do These Two Medicines Compare?

Are semaglutide and tirzepatide the same medicine?

No. Tirzepatide is not a form of semaglutide, and the two are not interchangeable. They belong to the same broad class of weight-loss medicines but are distinct molecules with different targets. If you have seen questions like whether tirzepatide and semaglutide are the same thing, the short answer is: they share a family resemblance but are chemically separate compounds.

Semaglutide (UK brand name Wegovy for weight loss) acts on the GLP-1 receptor — a pathway that regulates appetite, slows gastric emptying and influences how the brain processes hunger signals. Tirzepatide (UK brand name Mounjaro) does all of that and also activates the GIP receptor, which plays its own role in energy balance and fat storage. Hitting both receptors appears to produce a more pronounced response in many people, which is reflected in the trial data, and if you want to dig into whether semaglutide holds up against tirzepatide across those measures, the comparison is covered in detail.

One thing worth noting: Ozempic is also semaglutide, but it is licensed in the UK for type 2 diabetes, not weight management. Rybelsus is oral semaglutide, again licensed for diabetes. For weight loss, the relevant semaglutide product is Wegovy.

What does the trial evidence say about weight loss on each?

Both medicines have been tested in large, rigorous randomised trials, and the results are meaningful. In the STEP 1 trial (68 weeks, semaglutide 2.4mg), participants lost an average of around 15% of their body weight, as reported in the New England Journal of Medicine. In the SURMOUNT-1 trial (72 weeks, tirzepatide 15mg), the average reduction reached around 20–21%, also published in the NEJM. NICE's appraisal of tirzepatide (TA1026, published December 2024) noted that indirect comparisons favour tirzepatide over semaglutide for weight loss.

The most direct evidence comes from SURMOUNT-5, a 72-week head-to-head trial published in the New England Journal of Medicine in 2025, involving 751 adults with obesity and no diabetes. Tirzepatide produced a greater average weight reduction than semaglutide 2.4mg. That said, there is real variation between individuals. Some people do extremely well on semaglutide; some find the side-effect profile of tirzepatide less comfortable. Average figures from a trial population do not tell you what will happen to you specifically.

Do semaglutide and tirzepatide cause the same side effects?

Their side-effect profiles are similar, because both slow the passage of food through the gut. Nausea, indigestion, constipation, loose stools and fatigue are common to both, most noticeable after a dose increase and often settling within the first couple of weeks. The NHS tirzepatide page and the equivalent semaglutide page both detail what to watch for.

The MHRA has highlighted acute pancreatitis as a known but infrequent risk across GLP-1 medicines. Seek urgent medical attention for severe stomach pain that spreads to your back, with or without vomiting, that applies to both treatments equally. Neither medicine is recommended during pregnancy, while breastfeeding, or if you are trying to conceive. Both are prescription-only for under-18s (and neither is licensed for that age group). A full picture of contraindications and interactions (including the guidance on oral contraceptives and tirzepatide specifically) is something a prescriber will go through with you.

Thinking about switching direction? There is a separate question of moving from semaglutide to tirzepatide if you are already established on one treatment. That, too, needs clinical input.

Which should you choose, and what does a private prescription route look like?

There is no single right answer here. Tirzepatide's trial figures are stronger on average, but semaglutide has a longer track record and suits some people better in practice. A lot depends on your weight-related conditions, other medicines you take, and how you respond in the early weeks. Our prescribers look at the full picture before recommending anything, and the comparison of which medicine tends to perform better for different profiles is worth reading before your consultation.

On cost, both have seen price shifts in the private market. Eli Lilly raised Mounjaro's UK list price from September 2025, with the highest-dose pen rising from around £122 to around £330; typical private prices since then range roughly £149–£375 per month across doses and providers. For a fuller breakdown, the page on which is cheaper, Mounjaro or Wegovy, sets out what private prices typically include and what they often omit. At nume, one price covers the consultation, prescription, treatment, delivery and aftercare. We are not the cheapest option in the market, and that is a deliberate position, not an oversight.

Both pens are refrigerated (keep them in the fridge door so they are easy to spot and less likely to get jostled), though each has a limited window for room-temperature use if you are travelling, check the patient information leaflet for your specific medicine. Storage practicalities are worth factoring into your preference.

To see which of these medicines might be suitable for you, start your free consultation and a GPhC-registered prescriber will review your answers the same day.