Mounjaro, Wegovy and the rest: what's actually different?

Ask three people which weight-loss jab is "the strong one" and you'll get three answers. The names blur together — Mounjaro, Wegovy, Ozempic, now a Wegovy pill — yet the medicines behind them are genuinely distinct. This is the UK's weight-loss injections compared properly: what's in each one, what the trials measured, and what each costs from regulated providers. All are prescription-only medicines, and nothing here is medical advice.

Three treatments, two molecules

The UK private market currently revolves around three licensed options. Wegovy is a once-weekly injection of semaglutide. Mounjaro is a once-weekly injection of tirzepatide. And since its MHRA approval on 11 June 2026, the Wegovy pill — oral semaglutide — offers the same molecule as Wegovy in a daily tablet, the UK's first needle-free GLP-1 for weight loss. (Ozempic is semaglutide too, but licensed for type 2 diabetes rather than weight management.) So the real comparison comes down to two molecules and two delivery methods.

One hormone or two: the core difference

Semaglutide mimics a single gut hormone, GLP-1, which your body releases after eating. It acts on appetite centres in the brain to dial down hunger, increases fullness, and slows how quickly the stomach empties — so you simply eat less.

Tirzepatide does that and something extra: it mimics GIP as well, a second gut hormone, which is why it's sometimes called a "twincretin". Targeting both hormones at once is thought to be why Mounjaro tends to produce more weight loss on average than GLP-1-only medicines.

The Wegovy pill is chemically the same story as the Wegovy injection, with one engineering twist: an absorption enhancer (SNAC) in each tablet so the semaglutide survives the stomach. That's why it demands a strict morning routine — swallowed on an empty stomach with a small sip of water, then a 30-minute wait before food, drink or other tablets.

Weight-loss injections compared at a glance

Cheapest listed price across the regulated UK providers we track · prices last checked 4 July 2026 · full live tables on the homepage.

What the trials actually found

Mounjaro holds the headline numbers. In SURMOUNT-1 — adults with obesity or overweight, without type 2 diabetes — average loss over 72 weeks was 16.0% at 5 mg, 21.4% at 10 mg and 22.5% at 15 mg, against 2.4% on placebo.

Wegovy's STEP 1 trial produced a mean loss of about 14.9% over 68 weeks at 2.4 mg. When the two met head-to-head in SURMOUNT-5, tirzepatide averaged roughly 20% against roughly 14% for semaglutide — a real gap, though narrower than the separate trials implied.

The Wegovy pill's OASIS 4 trial reported about 13.6% average loss over 64 weeks at 25 mg — about 16.6% among people who took it consistently.

Two caveats keep these numbers honest. Averages hide enormous individual variation. And Wegovy holds a card Mounjaro doesn't yet: the SELECT trial showed it cut heart attack and stroke risk in people with existing heart disease — the only weight-loss jab with that evidence.

The dose ladders run at different speeds

All three start low and climb, because a gentle ramp is the main defence against nausea. But the ladders differ.

• Mounjaro starts at 2.5 mg weekly — a run-in dose, not a treatment dose — then steps up through 5, 7.5, 10 and 12.5 mg, each held at least 4 weeks, to a maximum of 15 mg.
• Wegovy takes about 16 weeks to reach its usual 2.4 mg maintenance dose. Since January 2026 the MHRA has also approved a higher 7.2 mg weekly dose for obesity only.
• The Wegovy pill climbs from 1.5 mg daily through 4 and 9 mg to 25 mg — roughly 12 weeks to full dose.

The practical difference is routine: a weekly pen is seconds of admin; the tablet is a daily commitment with an empty-stomach rule. Which you'll stick to for a year is the better question.

Side effects: more alike than different

Here the family resemblance dominates. Nausea, diarrhoea, constipation and vomiting lead the list for all three, concentrated around dose increases and usually settling as the body adjusts. Wegovy's trials logged nausea in roughly 40% of participants; Mounjaro and the pill sit in similar territory. The rare-but-serious list — pancreatitis, gallstones, dehydration — is also broadly shared, none are suitable during pregnancy, and a prescriber screens for the rest. We've unpacked the genuine differences in our side-effects comparison.

And the price gap?

The starting lines are far apart: Wegovy's 0.25 mg starter can be had from £79.97 for 4 weeks, the pill from £99, while Mounjaro's starter month begins at £145.99. At the top of each ladder the order holds — Wegovy 2.4 mg from £174.99, the pill's 25 mg from £190, Mounjaro 15 mg from £288.99.

The bigger money trap is choosing a provider carelessly rather than the "wrong" drug: the same 1 mg Wegovy dose spans £109 to £199 across the providers we track — a £90-a-month spread for an identical pen. Our full price comparison maps those gaps dose by dose.

So which one is "best"?

Wrong question, honestly. Best on trial-average weight loss is Mounjaro; best-established, with cardiovascular evidence, is Wegovy; best for the needle-averse is the pill. What fits you depends on your history, your tolerance for routine, and your budget over a year rather than a month. Our five-question choosing framework walks through that decision, and our 2026 ranking names a pick for each type of buyer. The final word always belongs to a prescriber.

Frequently asked questions

Are Mounjaro and Wegovy the same type of drug?

They belong to the same family but are different medicines. Wegovy contains semaglutide, which mimics one gut hormone (GLP-1). Mounjaro contains tirzepatide, which mimics two (GIP and GLP-1). They are not interchangeable brands of the same molecule, and switching between them is a prescriber's decision.

Which weight-loss injection produces the most weight loss?

On trial averages, Mounjaro. In the SURMOUNT-5 head-to-head trial, tirzepatide averaged about 20% weight loss against about 14% for semaglutide (Wegovy). These are averages, not guarantees — individual results vary widely.

Is the Wegovy pill as effective as the injections?

It gets close to the Wegovy injection but sits below Mounjaro. In the OASIS 4 trial, the 25 mg tablet averaged about 13.6% weight loss over 64 weeks — about 16.6% among consistent takers. The trade-off is a strict empty-stomach morning routine with a 30-minute wait before eating.

Do all three treatments cost about the same in the UK?

No. Across the providers we track, starter doses run from £79.97 (Wegovy) and £99 (Wegovy pill) to £145.99 (Mounjaro) per 4 weeks; top doses from £174.99, £190 and £288.99 respectively. Prices change often — confirm on the provider's site.