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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Which Mounjaro dose works best for weight loss?
The "best" Mounjaro dose depends on your individual health, how your body responds, and clinical assessment by your prescriber. Mounjaro is a prescription weight loss injection licensed in the UK, available as a weekly weight loss injection in doses ranging from 2.5 mg to 15 mg. Clinical trials showed that higher doses produced greater average weight loss, but individual results vary significantly. This guide compares Mounjaro dosing with Wegovy (an alternative prescription weight loss UK option) to help you understand how these medications work and what prescribers consider when choosing your dose.
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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 vs Wegovy: dose schedules and trial results
Mounjaro and Wegovy both require dose titration — starting low and increasing gradually. Mounjaro starts at 2.5 mg weekly and escalates every 4 weeks, reaching a maximum of 15 mg. Wegovy begins at 0.25 mg and escalates more slowly, reaching 2.4 mg maximum. The SURMOUNT-1 clinical trial showed Mounjaro at 15 mg produced average weight loss of approximately 20.9% of body weight over 72 weeks, whilst the STEP-1 trial showed Wegovy at 2.4 mg achieved approximately 14.9% average weight loss. These differences reflect their different mechanisms: Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy activates only the GLP-1 pathway. Both trials included reduced-calorie diet and increased physical activity. Individual weight loss outcomes vary significantly — some patients lose more at lower doses, whilst others need higher doses. A prescriber will assess which dose schedule suits your health profile.
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Three simple steps to understand your weight and take action.
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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How prescribers choose your Mounjaro dose
Your prescriber will not simply start you at the "best" dose — they follow a Mounjaro dose titration schedule for safety and tolerability. Typical progression involves 4 weeks at each dose level before escalation. Most patients respond well at 5 mg or 10 mg; some require 15 mg for optimal results, whilst others maintain effective weight loss at lower doses. Your GP or prescriber considers your BMI, existing health conditions, medication interactions, and how you tolerate side effects. Nausea, diarrhoea, and constipation are common during titration — these often settle as your body adjusts. If side effects are significant, your prescriber may pause escalation or reduce your dose. This personalised approach is why there is no single "best" dose for everyone. Use our free GLP-1 weight loss calculator to explore projected outcomes at different doses, and discuss your individual Mounjaro dose plan with your prescriber during clinical assessment.
- 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.
What's the starting dose of Mounjaro for weight loss?
The starting dose is 2.5 mg once weekly. You remain on this dose for 4 weeks before potentially escalating. This low starting dose allows your body to adjust and helps minimise side effects like nausea and digestive changes. Your prescriber will only increase your dose if you tolerate it well.
Is 15 mg Mounjaro always better than lower doses?
No. Clinical trials showed 15 mg produced the highest average weight loss, but higher dose doesn't assures better individual results. Some people achieve significant weight loss at 5 mg or 10 mg and experience fewer side effects. Your prescriber tailors your dose to your needs, not trial averages.
How does Mounjaro dosing compare to Wegovy dosing?
Mounjaro reaches 15 mg maximum in about 20 weeks, whilst Wegovy reaches 2.4 mg in about 16 weeks. Mounjaro escalates faster because it's a more potent dual-mechanism injection. Both require weekly dosing. Mounjaro produced higher average weight loss in trials, but individual suitability varies.
Can I stay on a lower Mounjaro dose if it's working?
Yes. If you're losing weight consistently and tolerating a lower dose well, your prescriber may recommend staying at that dose rather than escalating. Weight loss medication is personalised — there's no requirement to reach the maximum dose if you're achieving your health goals.
Why does Mounjaro dose titration take so long?
Gradual titration allows your body to adapt to the medication and reduces side effects. Starting low and increasing slowly also helps your prescriber identify your optimal dose — the lowest dose that produces meaningful weight loss with tolerable side effects for you specifically.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.