Mounjaro (tirzepatide) and Saxenda (liraglutide) are both injectable GLP-1 receptor agonists prescribed for weight management in the UK. But they differ significantly in how they work, how much weight loss they produce, their side effect profiles, and their cost. This guide compares them head-to-head to help you make an informed decision.
| Feature | Mounjaro (tirzepatide) | Saxenda (liraglutide) |
|---|---|---|
| Drug class | GIP + GLP-1 dual agonist | GLP-1 agonist |
| Injection frequency | Once weekly | Once daily |
| Starting dose | 2.5mg | 0.6mg |
| Maximum dose | 15mg | 3mg |
| Average weight loss | ~20% body weight | ~8% body weight |
| UK licence | Weight management (NICE approved) | Weight management |
| Cheapest monthly price | From ~£139/month | From ~£169/month |
| NHS availability | Limited (specialist referral) | Limited (specialist referral) |
Saxenda (liraglutide) is a GLP-1 receptor agonist — it mimics the GLP-1 hormone that signals fullness to the brain, slows gastric emptying, and reduces appetite. It was the first injectable weight loss treatment to gain widespread use in the UK.
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates both the GIP and GLP-1 pathways simultaneously. This dual action appears to produce significantly greater weight loss than GLP-1 agonists alone, which is why clinical trials show roughly double the weight loss compared to semaglutide and liraglutide.
| Treatment | Trial | Average Weight Loss | % Achieving ≥15% Loss |
|---|---|---|---|
| Mounjaro 15mg | SURMOUNT-1 | ~22.5% body weight | 57% |
| Mounjaro 10mg | SURMOUNT-1 | ~19.5% body weight | 49% |
| Saxenda 3mg | SCALE Obesity | ~8.4% body weight | 14% |
| Placebo | — | ~2.4% body weight | 2% |
In clinical trials, Mounjaro produced roughly 2.5× more weight loss than Saxenda at equivalent treatment durations. However, individual results vary and both treatments require lifestyle changes to be effective.
Both treatments share similar GI side effects, particularly during dose escalation. These typically improve after the first few weeks at each dose level.
| Side Effect | Mounjaro | Saxenda |
|---|---|---|
| Nausea | Very common (>10%) | Very common (>10%) |
| Vomiting | Common (1–10%) | Common (1–10%) |
| Diarrhoea | Common (1–10%) | Common (1–10%) |
| Constipation | Common (1–10%) | Less common |
| Injection site reactions | Common | Common |
| Hypoglycaemia (without diabetes meds) | Uncommon | Uncommon |
| Pancreatitis (rare) | Rare | Rare |
Saxenda requires a daily injection versus Mounjaro's weekly pen, which affects both convenience and cost. Saxenda pens contain 18mg of liraglutide and last approximately 6 days at the 3mg maintenance dose, meaning you need around 5 pens per month. Mounjaro is one pen per month regardless of dose.
| Treatment | Monthly Cost (Private UK) | Discount Codes Available |
|---|---|---|
| Saxenda 3mg (maintenance) | £169–£299/month | Yes — see our Saxenda page |
| Mounjaro 2.5mg (starting) | £139–£249/month | Yes — see our Mounjaro page |
| Mounjaro 15mg (maintenance) | £219–£369/month | Yes — see our Mounjaro page |
For most people seeking maximum weight loss, Mounjaro is the stronger option based on clinical evidence. It produces roughly double the weight loss of Saxenda, requires only a weekly injection, and is now available at comparable or lower prices from many UK pharmacies.
Saxenda may be preferred if you have previously tolerated liraglutide well (e.g. Victoza for diabetes), if your prescriber recommends it specifically, or if Mounjaro is temporarily out of stock at your preferred pharmacy.
Always consult a qualified prescriber before starting any injectable weight loss treatment. Both Mounjaro and Saxenda require a medical consultation and are not suitable for everyone.