Quick summary
- Ozempic (semaglutide) — licensed for type 2 diabetes; average weight loss 10–15%
- Wegovy (semaglutide, higher dose) — licensed for weight management; average weight loss 15–17%
- Mounjaro (tirzepatide) — dual GIP/GLP-1 agonist; average weight loss 18–22%
- All three are prescription-only, once-weekly injections available in the UK
- The best choice depends on your diagnosis, health profile and treatment goals
At a glance: the three medications compared
| Feature | Ozempic | Wegovy | Mounjaro |
|---|---|---|---|
| Active ingredient | Semaglutide | Semaglutide | Tirzepatide |
| Manufacturer | Novo Nordisk | Novo Nordisk | Eli Lilly |
| Mechanism | GLP-1 agonist | GLP-1 agonist | Dual GIP + GLP-1 agonist |
| UK licence | Type 2 diabetes | Weight management | Type 2 diabetes + weight management |
| Maintenance dose | 1–2 mg weekly | 2.4 mg weekly | 5–15 mg weekly |
| Dose-escalation period | 8 weeks | 16 weeks | Variable (minimum 20 weeks to max) |
| Avg. weight loss (clinical trials) | 10–15% | 15–17% | 18–22% |
| HbA1c reduction | Up to 1.8% | Up to 1.6% | Up to 2.4% |
| NHS availability | Diabetes only | Specialist weight mgmt services | Diabetes + specialist weight mgmt |
| Private cost (approx.) | £150–£250/month | £180–£300/month | £180–£350/month |
| CV outcomes data | Positive (SUSTAIN 6) | Positive (SELECT) | Ongoing (SURPASS-CVOT) |
How each medication works
Ozempic (semaglutide)
GLP-1 receptor agonist • Novo Nordisk
Ozempic targets the GLP-1 receptor, mimicking the natural incretin hormone released from the gut after eating. It stimulates glucose-dependent insulin secretion, suppresses glucagon, slows gastric emptying and acts on appetite centres in the brain. The maximum dose is 2 mg once weekly. While primarily licensed for type 2 diabetes, it produces clinically meaningful weight loss as a secondary benefit.
Wegovy (semaglutide, higher dose)
GLP-1 receptor agonist • Novo Nordisk
Wegovy contains the same active ingredient as Ozempic but at a higher maintenance dose of 2.4 mg, optimised for weight management. The higher dose provides greater appetite suppression. It is the first semaglutide product specifically licensed for chronic weight management in the UK and is recommended by NICE for use through NHS specialist weight management services.
Mounjaro (tirzepatide)
Dual GIP/GLP-1 receptor agonist • Eli Lilly
Mounjaro represents a different approach, activating both the GIP and GLP-1 receptors simultaneously. This dual mechanism enhances insulin secretion through complementary pathways, provides greater improvement in insulin sensitivity and produces the most significant weight loss of the three medications in clinical trials. It is licensed for both type 2 diabetes and weight management.
Effectiveness: weight loss results compared
Clinical trial data allows us to compare the weight loss achieved with each medication, although direct head-to-head comparisons between all three are limited.
Key trial results
| Trial | Medication | Duration | Avg. weight loss |
|---|---|---|---|
| SUSTAIN 1–6 | Ozempic (1 mg) | 30–56 weeks | 4.5–6.5 kg |
| STEP 1 | Wegovy (2.4 mg) | 68 weeks | 14.9% (~15 kg) |
| STEP 3 | Wegovy + IBT | 68 weeks | 16% (~16.5 kg) |
| SURMOUNT-1 | Mounjaro (15 mg) | 72 weeks | 20.9% (~24 kg) |
| SURMOUNT-1 | Mounjaro (10 mg) | 72 weeks | 19.5% (~22 kg) |
| SURPASS-2 | Mounjaro (15 mg) vs Ozempic (1 mg) | 40 weeks | 12.4 kg vs 6.2 kg |
It is important to note that trial populations, designs and durations differ, making direct cross-trial comparisons approximate rather than definitive. However, the consistent pattern across studies suggests that tirzepatide produces greater weight loss than semaglutide, which in turn is more effective than older GLP-1 agonists.
Blood sugar control compared
For patients with type 2 diabetes, glycaemic control is a primary consideration. All three medications significantly reduce HbA1c levels, but tirzepatide has demonstrated the greatest reductions in head-to-head comparisons.
- Ozempic: HbA1c reduction of approximately 1.5 to 1.8 percentage points
- Wegovy: HbA1c reduction of approximately 1.0 to 1.6 percentage points (lower than Ozempic in diabetes-specific trials, partly reflecting the different study populations)
- Mounjaro: HbA1c reduction of up to 2.4 percentage points at the 15 mg dose, with significantly more patients reaching an HbA1c below 7 per cent
Side effects compared
All three medications share a similar gastrointestinal side-effect profile, with nausea, vomiting, diarrhoea and constipation being the most common adverse effects. However, the severity and frequency vary.
Wegovy, with its higher semaglutide dose, tends to produce the highest rates of nausea (approximately 44 per cent in trials). Mounjaro's gastrointestinal side effects appear somewhat less frequent than Wegovy's, despite producing greater weight loss. Ozempic at lower doses has the mildest gastrointestinal profile of the three.
For detailed information about managing side effects, see our comprehensive GLP-1 side effects guide.
Cost comparison
Private costs for these medications vary by provider and dose. The following table provides approximate monthly costs at commonly used maintenance doses.
| Medication | Typical maintenance dose | Approx. monthly cost (private) |
|---|---|---|
| Ozempic | 1 mg | £200–£250 |
| Wegovy | 2.4 mg | £250–£300 |
| Mounjaro (5 mg) | 5 mg | £200–£250 |
| Mounjaro (10 mg) | 10 mg | £250–£300 |
| Mounjaro (15 mg) | 15 mg | £290–£350 |
On the NHS, patients pay the standard prescription charge (currently £9.90 per item in England, or free with a prepayment certificate, and free in Scotland, Wales and Northern Ireland).
NHS access: which can you get on the NHS?
For type 2 diabetes
Both Ozempic and Mounjaro are available on the NHS for type 2 diabetes when other treatments have not achieved adequate control. NICE guidance sets out specific eligibility criteria including HbA1c thresholds and BMI requirements.
For weight management
Both Wegovy and Mounjaro are available through NHS specialist weight management services (Tier 3) for patients meeting NICE eligibility criteria. Ozempic is not licensed for weight management and is therefore not available on the NHS for this purpose.
Note: Access to NHS weight management services varies across the country. Waiting times for Tier 3 services can be significant. Discuss options with your GP, who can advise on local referral pathways and estimated waiting times.
Which medication is right for you?
The choice between these three medications depends on several individual factors. There is no single best option for everyone.
Consider Ozempic if:
You have type 2 diabetes as your primary condition and need improved glycaemic control. Ozempic is well-established with extensive long-term safety data. It may be the most straightforward option if diabetes management is your main goal, with weight loss as a welcome secondary benefit.
Consider Wegovy if:
Weight management is your primary goal and you do not have type 2 diabetes (or it is well-controlled). Wegovy has strong NHS access through weight management services and is backed by the SELECT cardiovascular outcomes trial, which demonstrated significant heart health benefits in overweight and obese adults.
Consider Mounjaro if:
You are seeking the greatest possible weight loss, have type 2 diabetes requiring aggressive glycaemic control, or have not responded adequately to semaglutide. Mounjaro's dual mechanism produces the most significant results in clinical trials. It is available on the NHS for both diabetes and weight management.
Can I switch between medications?
Yes, switching between GLP-1 medications is possible and is sometimes recommended by clinicians if the initial medication is not well tolerated or is insufficiently effective. When switching, your prescriber will typically:
- Assess your response to the current medication
- Consider whether the switch is for efficacy or tolerability reasons
- Determine the appropriate starting dose of the new medication (which may not require a full dose escalation from the lowest dose, depending on your prior treatment)
- Monitor you for side effects during the transition
Never switch medications or adjust doses without consulting your prescriber.
Emerging treatments
The GLP-1 medication landscape continues to evolve rapidly. Several new treatments are in development or under regulatory review that may become available in the UK in the coming years:
- Oral semaglutide (Rybelsus): Already available for type 2 diabetes; higher doses for weight management are being studied
- CagriSema (semaglutide + cagrilintide): A combination of a GLP-1 agonist with an amylin analogue, currently in phase 3 trials
- Retatrutide: A triple GIP/GLP-1/glucagon agonist in clinical development showing weight loss exceeding 24 per cent
- Orforglipron: An oral non-peptide GLP-1 agonist in development by Eli Lilly
Frequently asked questions
Which weight loss injection has the fewest side effects?
All three medications share similar side-effect profiles. At their respective maintenance doses, Ozempic at 1 mg generally has the mildest gastrointestinal effects, while Wegovy at 2.4 mg tends to have the highest rates of nausea. Mounjaro appears to have a somewhat more favourable gastrointestinal tolerability profile than Wegovy despite greater weight loss, although individual experiences vary considerably.
Can I use these medications if I am not overweight?
These medications are prescription-only and are indicated for specific clinical conditions. They should not be used for cosmetic weight loss in people who are already at a healthy weight. Using these medications without appropriate medical supervision is not recommended and may be harmful.
How long do I need to take weight loss injections?
Current evidence suggests that these medications are most effective when used long-term. Clinical trials have shown that weight regain is common after discontinuation. NICE recommends ongoing treatment with regular clinical review. Your prescriber will work with you to determine the appropriate duration of treatment based on your response and individual circumstances.
Are generic or biosimilar versions available?
As of April 2026, no biosimilar versions of semaglutide or tirzepatide are available in the UK. The earliest biosimilar semaglutide products are expected to reach the market in the late 2020s, which may reduce costs. Always use medications sourced from a GPhC-registered pharmacy to avoid counterfeit products.