The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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Mounjaro vs Wegovy — Maintenance Doses in the UK
If you're considering weight loss treatment in the UK, you may be wondering whether Mounjaro or Wegovy is right for you. Both are prescription-only weight loss injections licensed in the UK, but they work differently and have different maintenance doses. Understanding the key differences — including how they're prescribed, their mechanisms, and trial outcomes — can help you have an informed conversation with your GP or prescriber about which might suit your needs.
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What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
How Mounjaro and Wegovy Differ — Mechanism and Trial Data
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two different hormone pathways to help regulate appetite and blood sugar. The SURMOUNT-1 clinical trial showed that on the maintenance dose of 15 mg once weekly, participants lost an average of 20.9% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single hormone pathway. The STEP-1 trial showed that at the maximum maintenance dose of 2.4 mg once weekly, participants achieved an average weight loss of approximately 14.9% of body weight at 68 weeks, again alongside lifestyle changes.
Both are once-weekly injections delivered via pre-filled pens. Mounjaro uses a KwikPen device, while Wegovy uses an auto-injection pen. Individual results vary significantly, and neither medication assures specific weight loss outcomes.
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Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
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Maintenance Doses and Suitability — A Prescriber Decision
Mounjaro maintenance dose: 15 mg once weekly (maximum). Doses escalate from 2.5 mg over 16+ weeks, with a minimum of 4 weeks at each dose level before increasing.
Wegovy maintenance dose: 2.4 mg once weekly (maximum). Dose escalates from 0.25 mg over 16+ weeks in smaller increments.
Both medications are prescription-only in the UK and require a clinical assessment before being prescribed. Your GP or a licensed prescriber will assess whether you're eligible — typically a BMI of 30 or above, or 27 or above with weight-related health conditions — and which medication might be more suitable for your individual circumstances, medical history, and any other medications you take.
Neither medication works alone: both are designed to be used alongside a reduced-calorie diet and increased physical activity. Once you reach your maintenance dose, you'll continue with once-weekly injections to help sustain weight loss. Use our free GLP-1 weight loss calculator to explore estimated weight loss outcomes at different doses, and our BMI calculator to check whether you may be eligible for either treatment based on your current weight and height.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Is Mounjaro or Wegovy more effective for weight maintenance?
Clinical trials show Mounjaro achieved slightly higher average weight loss (20.9% vs 14.9%), but individual results vary significantly. Effectiveness depends on your personal metabolism, adherence, diet, and exercise. Neither is assured to work for everyone. Your prescriber will help determine which suits your circumstances.
What's the difference between the maintenance doses?
Mounjaro's maximum maintenance dose is 15 mg once weekly. Wegovy's is 2.4 mg once weekly. The doses are not directly equivalent — Mounjaro has a dual mechanism while Wegovy has a single GLP-1 mechanism. Both escalate gradually from lower starter doses.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between medications must be managed by your prescriber. There's no official established conversion between doses — any change requires clinical assessment and a new prescription. Your GP or clinic will advise on the safest transition process for you.
How is Mounjaro prescribed on the NHS versus privately in the UK?
NHS access is through specialist tier 3 weight management services, typically via GP referral. Availability varies by region and waiting lists can be long. Private access is through GPhC-registered online pharmacies following an online clinical assessment. Both routes require a valid prescription.
Do I need to stay on the maintenance dose forever?
That's a decision between you and your prescriber. Some people stay on maintenance long-term to sustain weight loss; others may reduce or stop. The goal is usually to achieve weight loss, maintain it, and eventually transition to lifestyle changes alone — but this varies individually.
Ready to take control of your weight loss journey?
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