If you're considering weight loss injections in the UK, there are currently three licensed options: Mounjaro, Wegovy, and Saxenda. All belong to the GLP-1 medication class (with Mounjaro also targeting GIP), but they differ significantly in effectiveness, dosing, cost, and convenience. This guide puts all three side by side.
At a glance
| Mounjaro | Wegovy | Saxenda | |
|---|---|---|---|
| Active ingredient | Tirzepatide | Semaglutide | Liraglutide |
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist | GLP-1 agonist |
| Injection frequency | Once weekly | Once weekly | Once daily |
| Max dose | 15mg | 7.2mg | 3.0mg |
| Avg. weight loss | Up to 22.5% | Up to 20.7% | Up to 8% |
| Key trial | SURMOUNT-1 (72 weeks) | STEP UP (72 weeks) | SCALE (56 weeks) |
| CV evidence | Trial ongoing | SELECT: 20% MACE reduction | None for weight loss |
| UK private cost | £159–£359/mo | £99–£299/mo | £150–£230/mo |
| NHS availability | Phased rollout (Cohort 1+) | Tier 3 SWMS | Tier 3 SWMS |
| Contraception warning | Yes — affects oral pill/HRT | No | No |
| Manufacturer | Eli Lilly | Novo Nordisk | Novo Nordisk |
Effectiveness: the numbers
The weight loss differences between these three medications are substantial. At their maximum licensed doses over approximately 72 weeks of treatment:
- Mounjaro (15mg): Up to 22.5% average body weight loss in the SURMOUNT-1 trial. In the head-to-head SURMOUNT-5 trial against semaglutide 2.4mg, tirzepatide achieved 20.2% vs 13.7%.12
- Wegovy (7.2mg): Up to 20.7% in the STEP UP trial — the newer, higher dose approved by the MHRA in January 2026. At the standard 2.4mg dose, approximately 15%.3
- Saxenda (3.0mg): Approximately 8% in the SCALE trial over 56 weeks. Significantly less effective than the newer options, but still clinically meaningful.4
The gap between Mounjaro and Wegovy at their maximum doses is now quite small (roughly 20–22% each). The gap between either of them and Saxenda is much larger.
Convenience: weekly vs daily
Both Mounjaro and Wegovy are once-weekly injections, which most people find manageable and easy to build into a routine. Saxenda requires a daily injection, which is a significant practical difference — it means 365 injections per year versus 52. For many people, this is the deciding factor against Saxenda.
Side effects
All three share similar gastrointestinal side effects since they all work on GLP-1 pathways: nausea, diarrhoea, constipation, vomiting, and stomach pain. Nausea rates tend to be highest with Wegovy (~40–44%) and Saxenda (~40%), and somewhat lower with Mounjaro (~20–25%).567
Key differences to be aware of:
- Mounjaro: May reduce effectiveness of oral contraceptives and oral HRT — the MHRA recommends additional barrier contraception for 4 weeks after starting and after each dose increase5
- Wegovy (7.2mg): Dysaesthesia (tingling/pins and needles) reported as a new side effect at the higher dose6
- Saxenda: Increased heart rate is a recognised side effect not typically seen with the other two7
For detailed side effects for each medication, see our side effects viewer.
Cardiovascular protection
Wegovy has the strongest cardiovascular evidence. The SELECT trial demonstrated a 20% reduction in major adverse cardiovascular events (heart attack, stroke, cardiovascular death) in people with obesity and established cardiovascular disease — the first obesity medication to show this benefit.8
Mounjaro's dedicated cardiovascular outcomes trial (SURPASS-CVOT) is still ongoing. Saxenda does not have cardiovascular outcomes data specific to its use in weight management.
Cost
UK private prescription costs are broadly comparable for the weekly injections, with Saxenda slightly cheaper but less effective:
- Mounjaro: £159–£359/month
- Wegovy: £99–£299/month
- Saxenda: £150–£230/month
When you factor in effectiveness, Mounjaro and Wegovy offer significantly more weight loss per pound spent than Saxenda.
Which one should you choose?
For maximum weight loss: Mounjaro or Wegovy — both are in the same league at maximum doses.
For cardiovascular protection: Wegovy — proven benefit from the SELECT trial.
If you also have Type 2 diabetes: Mounjaro — licensed for both conditions.
If you can't tolerate Mounjaro or Wegovy: Saxenda — different enough (older-generation liraglutide) that some people tolerate it better, and daily dosing allows more granular dose adjustment.
On a budget: Saxenda is the cheapest injectable, but consider orlistat or Mysimba (tablets) if cost is the primary concern.
As always, the best choice depends on your individual health profile, preferences, and what your prescriber recommends after a full clinical assessment.