The UK's most complete GLP-1 guide
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- 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: Understanding UK Dose Escalation
If you're considering weight loss treatment in the UK, you've likely heard about both Mounjaro (tirzepatide) and Wegovy (semaglutide). A common question is how the doses compare and which one might be right for you. The key difference isn't just about how much the dose "goes up by"—it's that Mounjaro and Wegovy use different starting points, escalation schedules, and maximum doses because they're fundamentally different medications with different mechanisms. This guide breaks down the dose progression for both, explains the clinical trial data behind them, and helps you understand what these differences mean for weight loss outcomes. Both are prescription-only weight loss injections available in the UK, and your GP or a licensed prescriber will assess which is appropriate for your individual health.
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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.
Mounjaro and Wegovy Dose Schedules: Side-by-Side Comparison
Mounjaro (tirzepatide) starting dose is 2.5 mg, escalating weekly through 5 mg, 7.5 mg, 10 mg, 12.5 mg, and up to a maximum of 15 mg. Each dose is held for at least 4 weeks before increasing.
Wegovy (semaglutide) starts much lower at 0.25 mg, progressing through 0.5 mg, 1 mg, 1.7 mg, and reaching a maximum of 2.4 mg. Like Mounjaro, each dose is maintained for approximately 4 weeks.
The different dose ranges reflect a fundamental difference: Mounjaro is a dual GIP and GLP-1 receptor agonist—it activates two separate hormone pathways—while Wegovy is a GLP-1-only receptor agonist. This dual mechanism in Mounjaro means the starting and maximum doses are much higher than Wegovy's because the medication works through two separate biological pathways. In clinical trials, SURMOUNT data for Mounjaro showed average weight loss of approximately 15–21% of body weight at the 15 mg dose, whilst STEP trial data for Wegovy showed average weight loss of around 15% at the 2.4 mg dose. Try our GLP-1 weight loss calculator to estimate potential outcomes at different doses.
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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.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
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Which Medication Is Right for You? A Prescriber Decision
Neither Mounjaro nor Wegovy is universally "better"—suitability depends entirely on your individual health, medical history, and how your body responds. Both are available as once-weekly injections and both require a prescription-only assessment by a licensed prescriber or NHS specialist. In the UK, eligibility for either medication typically requires a BMI of 30 kg/m² or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or obstructive sleep apnoea. Use our BMI calculator to check your current BMI, then discuss prescription weight loss options with your GP or via a licensed online prescriber. Common side effects for both include nausea, diarrhoea, and constipation—these often reduce over time. If you're on certain medications, particularly oral contraceptives or diabetes treatments, your prescriber may need to adjust dosages or timing.
- 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.
Why does Mounjaro start at 2.5 mg whilst Wegovy starts at 0.25 mg?
Mounjaro and Wegovy work differently at a cellular level. Mounjaro activates both GIP and GLP-1 receptors (dual agonist), whilst Wegovy activates GLP-1 only. The dual mechanism means Mounjaro requires higher absolute doses to achieve comparable effects. Starting doses are set based on clinical trial safety data for each drug separately.
What's the maximum dose for each medication in the UK?
Mounjaro's maximum dose is 15 mg once weekly. Wegovy's maximum is 2.4 mg once weekly. Both are prescription-only, and your prescriber will determine the right dose for you based on your response and tolerability during the titration phase.
Do the STEP and SURMOUNT trials show one medication is better than the other?
Both showed significant weight loss, but trials used different designs and populations, so direct comparison isn't straightforward. SURMOUNT (Mounjaro) showed average weight loss of 15–21% depending on dose. STEP (Wegovy) showed around 15% average weight loss. Individual results vary considerably—some people lose more, others less.
Is Mounjaro or Wegovy available on the NHS in the UK?
Both are now approved by NICE for use within NHS specialist tier 3 weight management services. However, NHS access varies significantly by region, and waiting lists can be very long. Many people access these medications privately through GPhC-registered online prescribers, which provides faster access.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between medications is possible but must be managed by a prescriber—there is no official conversion chart because they work differently. Your prescriber will assess whether switching is appropriate, time the transition carefully, and monitor your response. Never self-manage a switch between prescription weight loss medications. ```
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