Both Mounjaro and Wegovy are GLP-1 medications prescribed privately in the UK for weight loss. But they're not identical. One works better for some people; the other for others.
This guide breaks down the clinical evidence, side effect profiles, cost, and NHS availability so you can make an informed choice.
The Science: How They Work
Wegovy (semaglutide):
- Activates one receptor: GLP-1 (glucagon-like peptide-1)
- Mechanism: Slows stomach emptying, increases satiety signals to the brain, improves blood sugar control
- Established for decades in diabetes (as Ozempic)
- Weight-loss indication (Wegovy) approved 2021
Mounjaro (tirzepatide):
- Activates two receptors: GLP-1 + GIP (glucose-dependent insulinotropic polypeptide)
- Mechanism: Same as Wegovy plus additional GIP pathway (enhances insulin secretion, improves metabolic function)
- Newer (approved 2022)
- More recent weight-loss approvals; still relatively new
In plain English: Mounjaro has two "levers" to pull; Wegovy has one. Theoretically, Mounjaro should be stronger. The evidence confirms this.
Head-to-Head Clinical Evidence
Weight Loss Results (12 months)
Wegovy (semaglutide 2.4mg weekly):
- Average weight loss: 10-15% of body weight
- Example: 100kg person loses 10-15kg
- Range: Some individuals lose as little as 5%; others lose 20%+
Mounjaro (tirzepatide 15mg weekly):
- Average weight loss: 15-22% of body weight
- Example: 100kg person loses 15-22kg
- Range: Some lose 10%; others lose 25%+
Verdict: Mounjaro produces 5-7% additional weight loss on average. Clinically meaningful difference.
Blood Sugar Control
Wegovy: Good (reduces HbA1c by 1-1.5%).
Mounjaro: Better (reduces HbA1c by 1.5-2%). Better for people with type 2 diabetes or prediabetes.
Verdict: Mounjaro superior for metabolic health if prediabetic/diabetic.
At a Glance
Side Effect Profiles
Most Common Side Effects (First 4 Weeks)
Both medications commonly cause:
- Nausea (30-40% of users)
- Constipation (20-30%)
- Reduced appetite (intended)
- Vomiting (5-10%)
- Diarrhoea (10-15%)
- Fatigue (15-20%)
These typically subside after 4 weeks as the body adjusts.
Serious (Rare) Side Effects
Both have similar rare risks:
- Pancreatitis (0.1-0.2%)
- Gallbladder issues (1-2%)
- Thyroid concerns (research ongoing)
- Dehydration (especially if not drinking enough)
Important: These are rare but serious. Both require medical supervision.
GLP-1 Specific Concerns
Ozempic/Wegovy: "Ozempic face" (rapid fat loss causing facial hollowing). Cosmetic, not dangerous.
Mounjaro: Less reported facial hollowing (possibly due to slightly slower initial weight loss, though this is anecdotal).
Reality: Both cause rapid weight loss. Skin can lag behind. This is cosmetic, not medical.
Nausea Comparison
Wegovy: Nausea is common first 2 weeks, usually mild, subsides.
Mounjaro: Similar nausea profile, possibly slightly more pronounced in first 4 weeks (anecdotal reports), but similar resolution.
Verdict: Nausea profiles are comparable. Individual variation is significant.
Dosing and Escalation
Wegovy (Semaglutide)
Starting dose: 0.25mg weekly
- Week 1-4: 0.25mg (very low, mostly checking tolerance)
- Week 5-8: 0.5mg
- Week 9-12: 1mg
- Week 13+: 1.7mg (standard therapeutic)
- Week 17+: 2.4mg (maximum, where most weight loss occurs)
Timeline to max dose: 16 weeks (4 months) of gradual escalation.
Mounjaro (Tirzepatide)
Starting dose: 2.5mg weekly
- Week 1-4: 2.5mg
- Week 5-8: 5mg
- Week 9-12: 7.5mg
- Week 13+: 10mg
- Week 17+: 15mg (maximum)
Timeline to max dose: 16 weeks (4 months) escalation (similar, but slightly faster progression at each step).
Key difference: Mounjaro reaches therapeutic doses faster. Wegovy has longer ramp-up.
Cost Comparison (UK Private)
Wegovy (Semaglutide)
- Private clinic cost: £180-220/month (fully escalated dose)
- Range: £150-250 depending on clinic
- Supply: Branded as Wegovy by Novo Nordisk
- Availability: Most UK private clinics stock this
Mounjaro (Tirzepatide)
- Private clinic cost: £220-280/month (fully escalated dose)
- Range: £200-320 depending on clinic
- Supply: Branded as Mounjaro by Eli Lilly
- Availability: Most large UK private clinics stock this
Difference: Mounjaro costs ~£40-60/month more (roughly 25-30% premium).
One-year cost:
- Wegovy: £2,160-2,640
- Mounjaro: £2,640-3,360
- Difference: £480-720/year
NHS Availability
Wegovy on NHS: Extremely limited. Some regions offer it; most don't. GP funding is postcode-dependent and heavily rationed.
Mounjaro on NHS: Nearly unavailable for weight loss (not yet approved as weight-loss indication on NHS). Some NHS diabetes clinics use it for diabetes; not for weight loss.
Reality: Both are private-access only for weight loss. NHS won't fund either consistently.
Who Should Choose Which?
Choose Wegovy if:
- Budget is primary concern (saves £40-60/month)
- You prefer slow, gentle escalation (lower early nausea risk)
- You're in a rush (actually, both same timeline)
- You want the most established track record (has longer history as Ozempic)
- Prior GLP-1 use makes you prefer familiar medication
Choose Mounjaro if:
- Weight loss is your priority (5-7% additional weight loss)
- You have prediabetes or type 2 diabetes (better metabolic control)
- You can afford slightly higher cost
- You want newer, potentially better mechanism (dual receptor)
- Prior GLP-1 trial showed modest results (might do better with stronger medication)
Choose based on trial if:
- You're uncertain which suits you better (start on Wegovy for cost/gentleness, switch to Mounjaro at month 3 if results plateau)
- You want to test tolerance before committing to pricier option (Wegovy is slightly cheaper to trial)
Real-World Efficacy: What to Expect
Week 1-2: Nausea, reduced appetite, appetite drops 30-50%.
Week 3-8: Nausea subsides, appetite suppression stabilises. Weight loss 0.5-1.5kg/week.
Month 3: Reach meaningful dose. Weight loss compounds: 4-6kg lost.
Month 6: Full escalation. Weight loss 8-12kg (Wegovy) or 12-16kg (Mounjaro).
Month 12: Total weight loss 10-15% (Wegovy) or 15-22% (Mounjaro).
Variation: Individual responses vary significantly. Some people lose 5%; others lose 25%+.
Making the Choice: Practical Framework
Decision tree:
-
Can I afford Mounjaro?
- Yes → Choose Mounjaro (better results, worth the premium)
- No → Choose Wegovy (still effective, cost-conscious)
-
Do I have prediabetes/diabetes?
- Yes → Mounjaro (better metabolic control)
- No → Either works; Mounjaro still slightly better results
-
Have I tried GLP-1 before?
- Yes, modest results → Mounjaro (stronger effect)
- No, first try → Wegovy (cost-effective entry point)
-
Do I want the newest/strongest available?
- Yes → Mounjaro
- Cost-conscious → Wegovy
Switching Between Them
Can you switch from Wegovy to Mounjaro? Yes. Most clinics allow switching if you're not seeing adequate results after 3-4 months on Wegovy. Some charge a consultation fee; others don't.
Timeline to switch: You'd stop Wegovy one week, start Mounjaro the next. No overlap. Restarting escalation takes 4 weeks, so expect restart time.
Strategy: Start Wegovy for cost, switch to Mounjaro at month 4 if plateau occurs. This de-risks the higher Mounjaro cost.
FAQ
Q: Which causes more side effects? Similar profiles. Individual variation is large. Can't predict who'll have more nausea.
Q: Which causes more "Ozempic face"? Both cause facial changes if weight loss is rapid. Mounjaro possibly slightly less (anecdotal), but this is cosmetic, not medical.
Q: Can I take both together? No. They work on similar pathways. Combining would increase side effect risk without benefit.
Q: Which is better for muscle preservation? Neither is ideal - both cause calorie deficit. High protein intake + resistance training preserve muscle on either medication. Supplement with protein powder.
Q: How quickly do I need to decide? Most clinics discuss options at consultation. You don't decide until you're ready to start. Shop around; get consultations with multiple clinics.
Q: If I lose weight, can I stop? Yes. Stopping is your choice anytime. Most people regain weight off the medication. Some maintain if lifestyle changes stick.
Which clinics prescribe each
Both medications are prescribed by the same UK private clinics, so your real choice is which clinic to trust rather than chasing a specific pen. Compare a few on price, the dose they titrate to, and the support included.
- Start with the clinic comparison and the best private GLP-1 clinics guide.
- For care designed around women, SheMed is worth comparing.
- To pair treatment with at home bloods, Rainbow Labs does both in one place.
These are editorial clinic links. We never sell prescription medication directly, and the right clinic depends on your own assessment.
My Recommendation
Start with: Wegovy - cost-effective, safe, proven, 10-15% weight loss is significant.
Upgrade to Mounjaro if:
- You can afford the £40-60/month premium
- You've been on Wegovy 3+ months with modest results (weight loss plateau)
- You want maximum results (15-22% average)
Practical strategy: Get Wegovy consultation first. Ask clinic if switching to Mounjaro is possible if needed. Start Wegovy, assess at month 3, decide then.
The Bottom Line
Both medications work. Mounjaro is stronger; Wegovy is cheaper. Choice depends on budget and goals.
For most people, Wegovy + high protein + resistance training + basic calorie deficit = excellent results.
For serious weight loss (15%+), Mounjaro is worth considering.
Talk to a private clinic (links in separate article). Get consultation, discuss both options. Decide based on your goals and budget.
Neither is available on NHS for weight loss. Both are available private within days. Start the process now if you're serious.
Find a clinic
Both Mounjaro and Wegovy are available through UK private clinics. Voy is the fastest for most people, with medication in 3 to 5 days. Lola Health is the strongest option for women wanting coaching alongside medication. For a women-focused service, SheMed is worth comparing.
For the full comparison, see the best private GLP-1 clinics guide and the clinic comparison page.
These are editorial clinic links. We never sell prescription medication directly.
Support products for the first weeks
Nausea and fatigue are worst in the first month on either medication. These are the products most women use to manage them.
Sea-Band Anti-Nausea Acupressure Wristbands (4-pack)
A four-pack of drug-free acupressure bands that press the Nei-Kuan point on the wrist. The cheapest, simplest thing to try in the first hours after your weekly injection when nausea peaks.
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Optimum Nutrition Gold Standard Whey 908g
24g of protein per scoop to help you hit your targets when your appetite is suppressed. Protein is the single most important lever for preserving muscle and limiting hair loss on a GLP-1.
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O.R.S Electrolyte Tablets
Pharmacy-grade oral rehydration tablets. When nausea or vomiting leaves you dehydrated, plain water is not enough, and replacing salts settles the dizziness and fatigue that follow.
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io Gut Health
Prebiotic fibre water for gut health
Some links above are affiliate links. If you buy through them we may earn a small commission, at no extra cost to you. It never changes what we recommend.
Resources
For clinic comparison and booking: see the best private GLP-1 clinics guide and the clinic comparison for full reviews and links.
For bloodwork baseline: Medichecks offers at-home hormone panels.
For supplement support: See "Best Supplements to Take on GLP-1" for protein, vitamins, and micronutrient protocols.