Wegovy vs Mounjaro
The two main GLP-1 weight loss treatments available in the UK, compared side by side. Costs, effectiveness, side effects, and where to get them.
At a Glance
| Wegovy (semaglutide) | Mounjaro (tirzepatide) | |
|---|---|---|
| Drug class | GLP-1 receptor agonist | Dual GIP/GLP-1 receptor agonist |
| Manufacturer | Novo Nordisk | Eli Lilly |
| Administration | Weekly subcutaneous injection | Weekly subcutaneous injection |
| NICE approved for weight loss | Yes (TA875) | Under review |
| MHRA licensed for weight loss | Yes | Licensed for type 2 diabetes; prescribed off-label for weight loss |
| Average weight loss (clinical trials) | 12-15% of body weight over 68 weeks (STEP trials) | 15-21% of body weight over 72 weeks (SURMOUNT trials) |
| Dose range | 0.25mg - 2.4mg (5 steps) | 2.5mg - 15mg (6 steps) |
| Typical starter cost | From GBP 99.97/month | From GBP 176.97/month |
| Maintenance cost | GBP 205 - 229/month | GBP 325 - 370/month |
| UK clinics offering | 6 providers | 5 providers |
Pricing from public clinic websites, March 2026. Costs vary by provider and may change. Clinical trial data from published peer-reviewed studies.
How They Work
Wegovy (Semaglutide)
Semaglutide mimics the GLP-1 hormone that your body produces naturally after eating. It slows gastric emptying (food stays in your stomach longer), reduces appetite signals to the brain, and improves blood sugar regulation.
Wegovy is the weight management brand of semaglutide (Ozempic is the same drug, branded for type 2 diabetes). It's the first GLP-1 to receive NICE approval specifically for weight management in the UK.
Mounjaro (Tirzepatide)
Tirzepatide is a "dual agonist" — it activates both GLP-1 and GIP receptors. GIP (glucose-dependent insulinotropic polypeptide) is a second gut hormone involved in appetite regulation and energy metabolism. Targeting both pathways appears to produce greater weight loss.
Mounjaro is currently licensed in the UK for type 2 diabetes. Its use for weight management is off-label but widely prescribed by CQC-registered clinics based on the SURMOUNT trial evidence.
Effectiveness: What the Evidence Shows
STEP Trials (Semaglutide / Wegovy)
The STEP programme was a series of phase 3 clinical trials involving over 4,500 participants. Key findings from STEP 1:
- Average weight loss of 14.9% of body weight over 68 weeks (vs 2.4% for placebo)
- 86.4% of participants achieved at least 5% weight loss
- 69.1% achieved at least 10% weight loss
- 50.5% achieved at least 15% weight loss
Source: Wilding et al., NEJM 2021. DOI: 10.1056/NEJMoa2032183
SURMOUNT Trials (Tirzepatide / Mounjaro)
The SURMOUNT programme studied tirzepatide for weight management in over 5,000 participants. Key findings from SURMOUNT-1:
- Average weight loss of 20.9% at the highest dose (15mg) over 72 weeks (vs 3.1% placebo)
- 15mg dose: 96% achieved at least 5% weight loss
- 15mg dose: 83.5% achieved at least 15% weight loss
- 15mg dose: 56.7% achieved at least 20% weight loss
Source: Jastreboff et al., NEJM 2022. DOI: 10.1056/NEJMoa2206038
Important: Clinical trial results represent averages across study populations. Individual results vary significantly based on factors including starting weight, diet, exercise, dose titration, and adherence. These are not guaranteed outcomes.
Side Effects
Both treatments share similar side effect profiles. Most side effects are gastrointestinal and tend to reduce as the body adjusts, particularly during dose escalation.
Common (affecting more than 1 in 10 people)
- Nausea (most common, usually worst during dose increases)
- Diarrhoea
- Constipation
- Vomiting
- Abdominal pain
- Headache
- Injection site reactions
Serious but rare
- Pancreatitis (inflammation of the pancreas)
- Gallbladder problems (gallstones)
- Kidney problems (usually from dehydration due to vomiting/diarrhoea)
- Allergic reactions
- Changes in heart rate
Both treatments carry a boxed warning about medullary thyroid carcinoma risk (observed in animal studies). They are contraindicated in patients with a personal or family history of MTC or Multiple Endocrine Neoplasia syndrome type 2.
Your prescriber will assess your medical history and discuss potential side effects before prescribing. Report any concerning symptoms to your prescriber or call NHS 111.
Eligibility
Wegovy (NICE criteria — TA875)
- BMI of 30 or above, OR
- BMI of 27 or above with at least one weight-related condition (e.g. type 2 diabetes, high blood pressure, obstructive sleep apnoea)
- Adults aged 18+
- Used alongside a reduced-calorie diet and increased physical activity
- Treatment reviewed at 6 months — continued if at least 5% weight loss achieved
Mounjaro (private clinic criteria)
- Criteria vary by clinic but typically mirror Wegovy eligibility
- BMI of 30 or above, OR BMI of 27+ with weight-related conditions
- Adults aged 18+
- Prescribed off-label for weight management (licensed for type 2 diabetes)
- Full medical assessment required before prescribing
Not suitable if you: are pregnant or breastfeeding, have a personal or family history of medullary thyroid carcinoma or MEN2, have type 1 diabetes, have severe gastrointestinal disease, or have a history of pancreatitis. Full contraindications are assessed during your consultation.
Cost Comparison by Clinic
Prices shown are monthly costs from public clinic websites. All include an online consultation with a prescriber. Prices may vary — always check the clinic's website for current pricing.
Wegovy (Semaglutide)
| Clinic | CQC Rating | Starter dose | Maintenance dose |
|---|---|---|---|
| Boots Online Doctor | Not yet inspected | GBP 99.97 0.25mg | GBP 205.97 2.4mg |
| Numan | Good | GBP 139.00 0.25mg | GBP 229.00 2.4mg |
| Juniper | Not yet inspected | GBP 164.00 0.25mg | GBP 229.00 2.4mg |
| Manual | Not yet inspected | GBP 229.00 0.25mg | GBP 229.00 0.25mg |
Mounjaro (Tirzepatide)
| Clinic | CQC Rating | Starter dose | Maximum dose |
|---|---|---|---|
| Boots Online Doctor | Not yet inspected | GBP 176.97 2.5mg | GBP 334.97 15mg |
| LloydsPharmacy Online Doctor | Good | GBP 190.00 2.5mg | GBP 325.00 15mg |
| Superdrug Online Doctor | Good | GBP 195.00 2.5mg | GBP 370.00 15mg |
| Juniper | Not yet inspected | GBP 199.00 2.5mg | GBP 339.00 15mg |
| Numan | Good | GBP 229.00 2.5mg | GBP 339.00 15mg |
Prices checked March 2026. All prices include online prescriber consultation. Delivery charges may apply. Some clinics offer discount codes — check their websites for current offers.
Which Treatment Is Right for You?
Consider Wegovy if...
- You want the treatment with full NICE approval for weight management
- You prefer a lower starting cost (from GBP 99.97/month)
- You want NHS availability as an option (limited but expanding)
- You want the most extensive long-term safety data
Consider Mounjaro if...
- You want the treatment with the highest average weight loss in clinical trials
- You're comfortable with an off-label prescription (widely prescribed, but not yet NICE-approved for weight management)
- You have a higher budget (from GBP 176.97/month)
- You've tried semaglutide and want to explore the dual-agonist mechanism
This is not medical advice. The choice between treatments should be made with your prescriber, who will consider your medical history, BMI, existing conditions, and personal circumstances. Both treatments are effective — the right one is the one that works for your situation.
Sources
- NICE Technology Appraisal TA875 — Semaglutide for managing overweight and obesity (June 2023)
- Wilding JPH et al. "Once-Weekly Semaglutide in Adults with Overweight or Obesity." NEJM 2021; 384:989-1002
- Jastreboff AM et al. "Tirzepatide Once Weekly for the Treatment of Obesity." NEJM 2022; 387:205-216
- NHS — Obesity: identification, assessment and management (CG189)
- MHRA — Summary of Product Characteristics: Wegovy (semaglutide), Mounjaro (tirzepatide)
- Clinic pricing from public provider websites, verified March 2026