What are Wegovy and Mounjaro?
Wegovy and Mounjaro are weekly injectable medications that help control appetite and support weight loss by mimicking hormones released by your body after eating.
Both medications are approved by the UK’s Medicines and Healthcare products Regulatory Agency (MHRA) for treating:
- Obesity (BMI ≥30 kg/m²), or
- Overweight (BMI ≥27 kg/m²) with at least one weight-related health condition
Wegovy, manufactured by Novo Nordisk, contains semaglutide. It received UK approval in September 2022 and has a substantial safety record with millions of users worldwide.
Mounjaro, manufactured by Eli Lilly, contains tirzepatide. It received UK approval for weight management in November 2023, following initial approval for type 2 diabetes.
How these medications work
Both medications mimic naturally occurring hormones that regulate hunger and blood sugar, but they work in slightly different ways.
How Wegovy works
Wegovy mimics one hormone called GLP-1 (glucagon-like peptide-1), which has three main effects:
- Slows food movement through your stomach, helping you feel fuller for longer
- Communicates with your brain’s appetite control centre (the hypothalamus) to reduce hunger
- Improves blood sugar control by enhancing insulin function
The natural GLP-1 hormone in your body lasts only minutes before being cleared. Wegovy’s effects last for days, providing sustained appetite control.
Many people report that Wegovy reduces not just physical hunger but also ‘food noise’, the constant thoughts about food that can lead to overeating.
How Mounjaro works
Mounjaro works on two hormone systems instead of one:
- Like Wegovy, it activates the GLP-1 receptor
- It also activates a second receptor called GIP (glucose-dependent insulinotropic polypeptide)
This dual-action approach likely explains why Mounjaro produces greater average weight loss in clinical trials at standard doses.1 The additional GIP activation provides extra blood sugar control and hunger management.
Clinical trials vs real-world results
What the clinical trials show
The landmark SURMOUNT-5 trial published in 2025 directly compared these medications head-to-head at standard maximum doses:1
- Mounjaro (tirzepatide 15 mg) produced 20.2% average weight loss
- Wegovy (semaglutide 2.4 mg) produced 13.7% average weight loss
- The 6.5 percentage point difference was statistically significant
This trial used maximum approved doses at the time (Mounjaro 15 mg, Wegovy 2.4 mg) and lasted 72 weeks.
Second Nature’s real-world comparison
Clinical trials are the gold standard for comparing medications, but they don’t always reflect real-world outcomes – particularly when comprehensive support is provided alongside medication.
Second Nature’s peer-reviewed study published in JMIR Formative Research (2025) directly compared both medications within our programme:3
Tirzepatide (Mounjaro) cohort (n=209):
- 22.1% average weight loss at 12 months
- 95.2% achieved at least 10% weight loss
- 83.7% achieved at least 15% weight loss
Semaglutide (Wegovy) cohort (n=130):
- 17.1% average weight loss at 12 months
- 83.1% achieved at least 10% weight loss
- 56.2% achieved at least 15% weight loss
Both cohorts exceeded clinical trial results, suggesting that comprehensive behavioural support enhances outcomes regardless of which medication you use.
The difference between the two medications was smaller in real-world practice (5 percentage points) compared to the SURMOUNT-5 trial (6.5 percentage points), which may suggest that behavioural support helps narrow the gap.
What about Wegovy 7.2 mg?
A higher dose of Wegovy (7.2 mg) will be available soon, with recent research suggesting its weight-loss efficacy is comparable to that of Mounjaro 15 mg.
The STEP UP trial published in The Lancet Diabetes & Endocrinology compared Wegovy 7.2 mg against the standard 2.4 mg dose:2
| Outcome |
Wegovy 7.2 mg |
Wegovy 2.4 mg |
| Average weight loss |
20.7% |
17.5% |
| Achieved ≥20% weight loss |
50.9% |
35.1% |
| Achieved ≥25% weight loss |
33.2% |
16.7% |
How does Wegovy 7.2 mg compare to Mounjaro 15 mg?
At maximum doses, the two medications now produce very similar results:
- Wegovy 7.2 mg: 20.7% average weight loss (STEP UP trial)2
- Mounjaro 15 mg: 20.2% average weight loss (SURMOUNT-5 trial)1
This means that if maximum weight loss is your primary goal, both medications can now achieve comparable results when used at their highest doses.
The 7.2 mg dose is delivered in three 2.4 mg pens and is suitable only for individuals who have titrated through the standard doses and tolerated 2.4 mg well. It’s not a starting dose.
For a detailed comparison of Wegovy doses, see our guide to Wegovy 7.2 mg vs 2.4 mg.
Side effects and tolerability
Both medications have similar side-effect profiles, primarily affecting the gastrointestinal tract. Most side effects are mild to moderate and improve over time.
| Side effect |
Wegovy (semaglutide) |
Mounjaro (tirzepatide) |
| Nausea |
Common (31.5% at month 1)3 |
Common (27.8% at month 1)3 |
| Constipation |
Common (31.5% at month 1)3 |
Common (29.2% at month 1)3 |
| Fatigue |
Less common (24.6% at month 1)3 |
Common (21.5% at month 1)3 |
| Hair loss |
Uncommon (5.4% at month 12)3 |
Less common (9.6% at month 12)3 |
| No side effects reported (month 12) |
67.7%3 |
60.3%3 |
Side effects improve significantly over time
Second Nature’s research showed that side effects decrease substantially as your body adjusts to the medication:3
- Nausea dropped from 31.5% to 3.1% (semaglutide) and 27.8% to 10.5% (tirzepatide) by month 12
- Fatigue dropped from 24.6% to 3.1% (semaglutide) and 21.5% to 8.1% (tirzepatide) by month 12
- The proportion reporting no side effects increased significantly in both groups
Hair loss: what the research shows
Hair loss is often reported as a concern with weight-loss medications. Our research found it affected 5.4% of semaglutide users and 9.6% of tirzepatide users at 12 months.3
This is likely related to rapid weight loss rather than the medication itself. Hair follicles can temporarily enter a resting phase during significant weight loss. For most people, hair growth returns to normal once weight stabilises.
Side effects with Wegovy 7.2 mg
The STEP UP trial found that side effects were somewhat more common at the 7.2 mg dose compared to 2.4 mg:2
- GI side effects: 70.8% (7.2 mg) vs 61.2% (2.4 mg)
- Dysaesthesia (tingling/numbness): 22.9% (7.2 mg) vs 6.0% (2.4 mg)
- Discontinuation due to side effects remained low at 3.3%
The dysaesthesia finding is notable, though 85.7% of cases resolved while continuing treatment.
Practical differences
Beyond effectiveness and side effects, there are several practical considerations when choosing between these medications.
Dosing flexibility
Wegovy follows a fixed dose escalation schedule, typically progressing to the maintenance dose of 2.4 mg over 16-20 weeks. The newer 7.2 mg dose is available for those who need additional support beyond 2.4 mg, delivered as three 2.4 mg pens.
Mounjaro offers three maintenance dose options (5 mg, 10 mg, and 15 mg), giving you and your prescriber more flexibility to find the dose that balances effectiveness with tolerability.
Storage requirements
Both medications should be stored in the refrigerator (2-8°C) before first use. Once in use:
- Wegovy: Can be kept at room temperature (below 30°C) for up to 28 days
- Mounjaro: Can be kept at room temperature (below 30°C) for up to 21 days
For travel, both can be carried in hand luggage. If you’re travelling somewhere warm, consider using a cool bag or insulated pouch. Neither medication should be frozen.
What if you miss a dose?
Wegovy: If you miss a dose and there are more than 2 days until your next scheduled dose, take it as soon as you remember. If there are fewer than 2 days, skip the missed dose and take your next dose on the scheduled day.
Mounjaro: Similar guidance applies. If you miss a dose and there are at least 4 days until your next scheduled dose, take it as soon as you remember. Otherwise, skip the missed dose.
Injection technique
Both medications use pre-filled pens that are straightforward to use. Neither requires priming before each injection. You inject into the skin of your stomach, thigh, or upper arm, rotating sites to avoid irritation.
Cost and access in the UK
Private prescription costs
Costs vary between providers. At Second Nature, our all-inclusive programme (medication, delivery, dietitian support, and app access) costs:
- Mounjaro: £229-£349 per month depending on dose
- Wegovy: £149-£249 per month depending on dose (it’s unclear what the cost of Wegovy 7.2 mg will be)
- Wegovy 7.2 mg: £379 per month
Some pharmacy-only services offer lower per-pen prices but without comprehensive support. When comparing costs, consider what’s included and whether ongoing support might improve your long-term results.
NHS availability
Both medications are theoretically available through NHS specialist weight management services (Tier 3 and Tier 4), but access remains limited:
- Eligibility typically requires BMI ≥35 kg/m² (or ≥30 kg/m² with weight-related health conditions)
- Previous documented attempts at weight loss are usually required
- Waiting times vary significantly by region
- NHS England is currently expanding tirzepatide access following NICE guidance
Given these limitations, many eligible patients opt for private treatment.
Switching between medications
Why people switch
Common reasons for switching from Wegovy to Mounjaro include:
- Reaching a weight loss plateau on Wegovy
- Wanting to try the dual-action approach for potentially greater weight loss
- Better blood sugar control (particularly relevant for those with type 2 diabetes)
Common reasons for switching from Mounjaro to Wegovy include:
- Side effect concerns or poor tolerability with Mounjaro
- Cost considerations (Wegovy is typically less expensive)
- Preferring a medication with a longer safety track record
What about increasing the Wegovy dose instead of switching?
If you’re on Wegovy 2.4 mg and considering switching to Mounjaro for greater weight loss, the 7.2 mg dose offers an alternative. At maximum doses, both medications produce similar results (around 20% weight loss), so increasing your Wegovy dose may achieve comparable outcomes without changing medications.
How to switch safely
If you’re considering switching, always discuss this with your prescriber first. General guidance:
- There’s no need to ‘wash out’ one medication before starting the other
- You can typically switch directly from one medication to the other
- Your prescriber will advise on the appropriate starting dose based on your current dose
- Some weight fluctuation during the transition is normal
Who might prefer each option?
While individual responses vary significantly, certain factors might make one medication more suitable for your situation:
Wegovy might be preferred if:
- Cost is a concern – Wegovy is typically less expensive at standard doses
- You value a longer safety track record – Wegovy has been available longer
- You’ve responded well to other GLP-1 medications like Saxenda or Ozempic
- Side effect concerns are primary – Slightly higher proportion reporting no side effects at 12 months
- You want maximum weight loss on a single medication – The 7.2 mg dose now matches Mounjaro’s efficacy
Mounjaro might be preferred if:
- You want strong results at standard doses – Clinical trials and real-world data show greater average results without needing the highest dose
- You have type 2 diabetes alongside obesity – Particularly strong benefits for blood sugar control
- You’ve tried Wegovy without achieving desired results – The dual-action mechanism offers a different approach
- You want dosing flexibility – Three maintenance dose options available
Frequently asked questions
Which is more effective, Wegovy or Mounjaro?
At standard doses, Mounjaro produces greater average weight loss. The SURMOUNT-5 trial showed 20.2% vs 13.7% weight loss, and Second Nature’s real-world data showed 22.1% vs 17.1%.1,3
However, Wegovy 7.2 mg produces 20.7% weight loss, comparable to Mounjaro 15 mg at 20.2%.1,2
Individual responses vary considerably. Some people respond better to Wegovy, while others achieve better results with Mounjaro. The ‘best’ medication is the one that works for you.
Is Wegovy 7.2 mg as effective as Mounjaro 15 mg?
Yes, the clinical trial data suggest they produce very similar results. Wegovy 7.2 mg achieved 20.7% average weight loss in the STEP UP trial, while Mounjaro 15 mg achieved 20.2% in the SURMOUNT-5 trial.1,2
If you’re currently on Wegovy 2.4 mg and not reaching your goals, increasing to 7.2 mg may be an alternative to switching to Mounjaro.
Is Wegovy or Mounjaro safer?
Both medications have acceptable safety profiles and similar side effect profiles. Wegovy has a longer track record, as it was approved earlier.
Neither medication has shown significant safety concerns in clinical trials or real-world use when prescribed appropriately.
How long do I need to stay on these medications?
Current guidance suggests these medications are most effective when used long-term. NICE recognises obesity as a chronic condition and recommends treatment for at least 12 months, with potential continuation if safe and effective.6
Research shows that significant weight regain typically occurs when stopping medication without proper support and habit formation.7
Will I gain weight back after stopping?
Some weight regain is common after stopping either medication if sustainable habits haven’t been established. Clinical trials show that people typically regain approximately two-thirds of lost weight within a year of stopping, without ongoing support.7
This is why Second Nature’s programme focuses on building lasting habits alongside medication, to support weight maintenance after you stop.
Does either medication interact with contraception or HRT?
Both medications can affect the rate of oral drug absorption by slowing gastric emptying. If you take oral contraception, discuss with your prescriber whether alternative methods might be advisable during the first few months of treatment.
There’s no evidence of direct interaction with HRT patches or injections.
Can I drink alcohol while taking these medications?
Moderate alcohol consumption is generally fine with both medications. However, many people find that their alcohol tolerance decreases so that they may feel the effects of alcohol more quickly.
Both medications can cause nausea, and alcohol may worsen this. If you experience significant nausea, it’s best to limit alcohol until symptoms improve.
Is one better for people with PCOS or insulin resistance?
Both medications improve insulin sensitivity, which can benefit people with PCOS or insulin resistance. Mounjaro’s dual-action mechanism may provide additional benefits for blood sugar control, but both have shown positive effects.
Do these medications affect fertility?
Neither medication is recommended during pregnancy or while trying to conceive. Both manufacturers recommend stopping treatment at least 2 months before a planned pregnancy.
If you’re planning to start a family in the near future, discuss timing with your prescriber.
Can I switch from Wegovy to Mounjaro (or vice versa)?
Yes, switching is possible and relatively straightforward. You don’t need a ‘washout’ period between medications. Your prescriber will advise on the appropriate starting dose based on your current treatment.
Why do some people lose more weight than others on the same medication?
Weight-loss response depends on multiple factors, including genetics, baseline weight, medication adherence, dietary changes, physical activity, sleep quality, stress levels, and underlying health conditions.
This is why comprehensive programmes that address these factors tend to produce better results than medication alone.
Take home message
At standard doses, Mounjaro produces greater average weight loss than Wegovy (20.2% vs 13.7% in clinical trials).1 However, the introduction of Wegovy 7.2 mg means both medications support similar weight loss at their highest dose.1,2
Second Nature’s real-world data confirm that both medications achieve clinically significant weight loss for the vast majority of users: 95% with Mounjaro and 83% with Wegovy achieved at least 10% weight loss in our programme.3
The ‘best’ medication depends on your personal health profile, cost considerations, tolerance for side effects, and individual response.
If maximum weight loss is your priority and you’re willing to use the highest available dose, both medications can now achieve comparable results.
What matters most for long-term success is not just which medication you choose, but the support system and habit changes you develop alongside it.
Second Nature's Mounjaro and Wegovy programmes
Second Nature provides Mounjaro or Wegovy as part of our Mounjaro and Wegovy weight-loss programmes.
Why choose Second Nature over other medication providers, assuming you're eligible?
Because peace of mind matters.
We've had the privilege of working with the NHS for over eight years, helping people across the UK take meaningful steps toward a healthier, happier life.
Our programmes are designed to meet people where they are, whether that means support with weight loss through compassionate one-to-one health coaching, or access to the latest weight-loss medications (like Mounjaro and Wegovy) delivered alongside expert care from a multidisciplinary team of doctors, psychologists, dietitians, and personal trainers.
At the heart of everything we do is a simple belief: real, lasting change comes from building better habits, not relying on quick fixes. We're here to support that change every step of the way.
With over a decade of experience, thousands of lives changed, and a long-standing record of delivering programmes used by the NHS, we believe we're the UK's most trusted weight-loss programme.
We hope to offer you something invaluable: peace of mind, and the support you need to take that first step.
References
- Aronne LJ, Horn DB, le Roux CW, et al. Tirzepatide as compared with semaglutide for the treatment of obesity. N Engl J Med. 2025;393:26-36. https://www.nejm.org/doi/full/10.1056/NEJMoa2416394
- Wharton S, Freitas P, Hjelmesæth J, et al. Once-weekly semaglutide 7·2 mg in adults with obesity (STEP UP): a randomised, controlled, phase 3b trial. Lancet Diabetes Endocrinol. Published online September 14, 2025. https://www.thelancet.com/journals/landia/article/PIIS2213-8587(25)00226-8/abstract
- Richards R, Lunt W, Whitman M, et al. Semaglutide and tirzepatide in a remote weight management program: 12-month retrospective observational study. JMIR Form Res. 2025;9:e81912. https://formative.jmir.org/2025/1/e81912
- Wilding JP, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity. N Engl J Med. 2021;384(11):989-1002. https://www.nejm.org/doi/full/10.1056/NEJMoa2032183
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022;387(3):205-216. https://www.nejm.org/doi/full/10.1056/NEJMoa2206038
- National Institute for Health and Care Excellence. Tirzepatide for managing overweight and obesity (TA1026). 2024. https://www.nice.org.uk/guidance/ta1026
- Aronne LJ, Sattar N, Horn DB, et al. Continued treatment with tirzepatide for maintenance of weight reduction in adults with obesity: the SURMOUNT-4 randomized clinical trial. JAMA. 2024;331(1):38-48. https://jamanetwork.com/journals/jama/fullarticle/2812936
