Mounjaro vs Wegovy - Weight loss injections head to head
When choosing a weight loss injection, many people find themselves comparing Mounjaro and Wegovy, two of the most effective medications available. Both have proven track records for significant weight loss, but new clinical evidence shows clear differences in their performance that could influence your decision.
The most striking finding comes from the first direct head-to-head comparison study. After 72 weeks of treatment, people taking Mounjaro lost an average of 20% of their body weight, whilst those on Wegovy lost approximately 14%. This represents nearly half again as much weight loss with Mounjaro, making it substantially more effective for many patients.
How These Medications Work Differently
Both Wegovy and Mounjaro belong to a group of medicines called GLP-1 receptor agonists, but they work through different mechanisms. Wegovy contains semaglutide, which mimics a single hormone (GLP-1) that signals fullness to your brain after eating. This helps you feel satisfied with smaller portions and reduces cravings between meals.
Mounjaro takes a dual approach. Its active ingredient, tirzepatide, mimics both GLP-1 and a second hormone called GIP (glucose-dependent insulinotropic polypeptide). This dual action may explain why Mounjaro consistently outperforms Wegovy in clinical trials. The additional GIP receptor activation provides enhanced appetite suppression and may reduce some gastrointestinal side effects.
Here are the key differences at a glance:
- Active ingredients: Wegovy uses semaglutide (GLP-1 only), whilst Mounjaro uses tirzepatide (dual GLP-1 and GIP action)
- Dosing schedules: Wegovy starts at 0.25mg weekly, reaching a maximum of 2.4mg; Mounjaro begins at 2.5mg weekly and can go up to 15mg
- Mechanism: Single hormone mimicry versus dual hormone approach
- Weight loss potential: Mounjaro shows consistently higher weight loss percentages across all dose levels
- Side effect profiles: Similar overall, but Mounjaro may cause less nausea due to its GIP component
- NHS availability: Wegovy is available through NHS specialist services; Mounjaro approval is being rolled out gradually from June 2025
Weight Loss Results: The Numbers Tell the Story
The landmark clinical trial results reveal significant differences in effectiveness. Among participants who maintained treatment, 81.8% taking Mounjaro achieved at least 5% weight loss compared to 66.5% on Wegovy. The gap widens further with greater weight loss targets: 42.3% of Mounjaro users lost 15% or more of their body weight, whilst only 18.1% of Wegovy users reached this milestone.
Research published in major medical journals consistently shows Mounjaro's superior performance. A comprehensive analysis found that people taking the highest dose of Mounjaro (15mg) lost up to 22.5% of their body weight over 72 weeks, compared to 15% with Wegovy's maximum dose over 68 weeks. These results translate to meaningful differences for real patients – someone weighing 100kg might lose 20-23kg with Mounjaro versus 14-15kg with Wegovy.
Both medications do require time to show results. Wegovy users might see slightly faster initial effects, potentially losing up to 5% of body weight within the first month compared to 4% with Mounjaro. However, Mounjaro's advantage becomes clear over longer treatment periods, with the difference becoming more pronounced after six months of treatment.
Managing Side Effects and Treatment Experience
The side effect profiles of both medications are remarkably similar, as both slow gastric emptying and affect appetite-regulating pathways. The most commonly reported issues include nausea, constipation, diarrhoea, and abdominal discomfort. These typically appear when starting treatment or increasing doses, then often diminish as your body adjusts.
Interestingly, some evidence suggests Mounjaro may cause less intense nausea despite achieving greater weight loss. Dr Lofton, a weight management specialist, explains that "dual agonism from GIP provides more of a delay in gastric emptying and has a slight antiemetic effect," meaning it actually helps minimise nausea even whilst slowing stomach emptying.
Here are practical strategies for managing common side effects:
- Start with small, frequent meals rather than three large ones throughout the day
- Stay well-hydrated with clear fluids like water and herbal teas
- Avoid high-fat and heavily processed foods which can worsen nausea
- Consider over-the-counter remedies like ginger tea for stomach upset
- Plan injection timing around your schedule to minimise disruption from side effects
- Contact your prescriber if symptoms become severe or don't improve after several weeks
Serious side effects remain rare with both medications, occurring in fewer than 2% of users. These include pancreatitis, gallbladder problems, and kidney issues. Your healthcare provider will monitor you for these conditions and can adjust treatment if necessary.
Expert Insights on Treatment Choice
Leading diabetes specialists note the significance of having head-to-head comparison data. As researchers from Aristotle University of Thessaloniki observed after conducting a comprehensive analysis of 22 studies, "tirzepatide is superior to semaglutide for both blood sugar control and weight loss". This superiority appears consistent across different patient groups, including those with and without diabetes.
NHS England's interim commissioning guidance recognises both medications as effective treatments, with Mounjaro being introduced through a phased approach due to high demand and limited healthcare capacity. The guidance emphasises that access will be prioritised for those with the greatest clinical need, including people with BMI over 40 and multiple weight-related health conditions.
Clinical experts stress that individual responses can vary significantly. Dr Thomas Karagiannis's research team noted that while tirzepatide showed superior average results, some patients may respond better to semaglutide depending on factors like hormone levels, existing health conditions, and medication tolerance. This highlights the importance of working with your healthcare provider to find the most suitable option for your circumstances.
Real Patient Experiences
User reports from UK patients provide valuable insights into real-world treatment experiences. Many Mounjaro users describe "accelerated initial weight loss and a decrease in cravings," though some note more intense side effects during the first month of treatment. Wegovy users commonly report "gradual weight loss with good appetite control," with side effects typically being milder initially.
One pattern that emerges from patient feedback is that individuals switching from Wegovy to Mounjaro often experience improved outcomes, though the transition period requires careful management. As reported by UK treatment centres, "patients who opt to change to Mounjaro after taking Wegovy invariably experience improved outcomes, although it takes some time to transition".
The cost difference has become a significant consideration for private patients. From September 2025, Mounjaro prices increased substantially, with some doses now costing up to £330 per month compared to Wegovy's typical range of £100-200 monthly. This pricing shift has led many patients to consider Wegovy as a more accessible option whilst still achieving clinically meaningful weight loss.
Current UK Availability and Access
NHS access to these medications follows different timelines and criteria. Wegovy became available through NHS specialist weight management services in 2023, whilst Mounjaro approval began rolling out from June 2025. Both require meeting strict eligibility criteria, typically including BMI over 35 with weight-related health conditions or BMI over 40.
Private prescription costs vary significantly between providers. Wegovy generally costs £199-299 monthly, whilst Mounjaro ranges from £225-350 depending on dose and provider. Some services include additional support like nutritional coaching and lifestyle guidance, which can justify higher pricing.
The phased NHS rollout for Mounjaro prioritises patients with BMI over 40 and at least four weight-related conditions including type 2 diabetes, high blood pressure, heart disease, sleep apnoea, or abnormal blood fats. Due to limited NHS capacity, many eligible patients face waiting periods, leading some to choose private treatment initially.
| Feature | Wegovy (semaglutide) | Mounjaro (tirzepatide) |
|---|---|---|
| Hormone targets / class | GLP-1 receptor agonist (single-hormone) | Dual GIP + GLP-1 receptor agonist (two-hormone) |
| Injection frequency | Once weekly | Once weekly |
| Starting dose → max dose | 0.25 mg → 2.4 mg weekly (titrated) | 2.5 mg → 15 mg weekly (titrated) |
| Head-to-head average weight loss (~72 weeks) | ~14% body weight | ~20% body weight |
| % achieving ≥5% weight loss | 66.5% | 81.8% |
| % achieving ≥15% weight loss | 18.1% | 42.3% |
| Maximum trial-level result (highest dose) | ~15% at 68 weeks (2.4 mg) | ~22.5% at 72 weeks (15 mg) |
| Onset pattern | May see slightly faster initial loss (≈ up to 5% in month 1) | ≈ up to 4% in month 1; greater advantage beyond 6 months |
| Common side effects | Nausea, constipation, diarrhoea, abdominal discomfort | Similar profile; GI effects as above |
| Nausea tendency | Typical GLP-1-related nausea | May be less intense (GIP’s potential anti-emetic effect) |
| Serious adverse events | Uncommon (<2%): pancreatitis, gallbladder, kidney issues | Uncommon (<2%): pancreatitis, gallbladder, kidney issues |
| NHS availability (UK) | Available via specialist services since 2023 | Phased NHS rollout from June 2025 with prioritisation criteria |
| Private monthly price (typical) | ~£199–£299 (provider-dependent) | ~£225–£350; some doses ~£330 after Sep 2025 increase |
| Notable considerations | Strong appetite control; individual response varies | Higher average weight loss; dual-agonist may aid tolerability; individual response varies |
Key Takeaways
- Mounjaro demonstrates superior weight loss results, with users losing an average of 20% body weight versus 14% with Wegovy in direct comparison trials
- Both medications share similar side effect profiles, though Mounjaro may cause less nausea due to its dual hormone approach
- Cost considerations favour Wegovy for private patients, as recent price increases make Mounjaro significantly more expensive
- NHS access varies by location and eligibility, with Wegovy more widely available currently whilst Mounjaro rollout continues
- Individual responses vary, making consultation with healthcare providers essential for choosing the most appropriate treatment
The choice between these two effective medications ultimately depends on your individual circumstances, including weight loss goals, budget, NHS eligibility, and tolerance for side effects, all of which should be discussed thoroughly with your healthcare provider.
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