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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Why 2.5Mg Mounjaro Might Not Be Working — And How Wegovy Compares
If you're on 2.5mg Mounjaro and not seeing results, you're not alone — this is actually the starting dose and results typically emerge as you titrate to higher doses over several weeks. The difference between Mounjaro and Wegovy lies in their mechanisms and dose escalation, but both require time and patience. This guide explains why initial doses may feel ineffective and compares how Mounjaro and Wegovy work differently to help you understand what to expect next. Your prescriber can advise whether to continue titrating Mounjaro or explore other options based on your individual response.
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Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
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: Mechanisms, Doses, and Trial Data
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — meaning it activates two natural hormone pathways simultaneously. Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single pathway. Clinically, this dual mechanism in Mounjaro may produce greater weight loss in some individuals, though individual results vary significantly.
- Mounjaro starting dose: 2.5mg for weeks 1–4 (rarely produces noticeable effects at this stage)
- Wegovy starting dose: 0.25mg for weeks 1–4 (similarly minimal at initiation)
- SURMOUNT trial (Mounjaro): Average weight loss at 15mg was approximately 20.9% body weight over 72 weeks alongside diet and exercise
- STEP trial (Wegovy): Average weight loss at 2.4mg was approximately 14.9% body weight over 68 weeks with the same lifestyle support
Both medications require gradual dose escalation (titration) over 4–5 months before reaching maintenance doses where more significant weight loss typically occurs. Expecting results at the starting 2.5mg Mounjaro dose is unrealistic — this phase is about tolerability and side effect adjustment, not weight loss.
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How It Works
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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
What to Do If Mounjaro Isn't Working: Next Steps and Prescriber Discussion
If you're on 2.5mg Mounjaro and not seeing weight loss, the first step is to confirm you're still within the titration phase — this is expected. Discuss with your prescriber whether you're ready to escalate to the next dose (5mg in week 5). If side effects are preventing escalation, your prescriber may slow the titration schedule. If you've already reached higher doses (10mg+) and still have minimal response after 8–12 weeks, your prescriber may consider switching to an alternative medication like Wegovy or adjusting your approach.
Some individuals respond better to the single GLP-1 mechanism in Wegovy, whilst others tolerate the dual GIP+GLP-1 mechanism in Mounjaro better. Individual suitability is determined by your prescriber based on your response, medical history, and side effect tolerance — not by trial averages. Use our GLP-1 weight loss calculator to project potential outcomes at different doses, which may help guide your conversation with your prescriber.
- 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 2.5mg Mounjaro supposed to cause weight loss?
No — 2.5mg is the starting titration dose designed for tolerability and side effect assessment, not weight loss. Meaningful weight loss typically begins at 5–10mg doses after several weeks of titration. If you've only just started, continue as directed and discuss escalation timing with your prescriber.
How long does it take for Mounjaro to work?
Initial side effects often appear within days, but weight loss typically becomes noticeable at 5–10mg doses after 6–8 weeks of use. Full efficacy is usually reached at 15mg (maximum dose). Total treatment time from start to visible results is typically 4–6 months with proper titration.
Should I switch from Mounjaro to Wegovy if Mounjaro isn't working?
That's a decision for your prescriber. Wegovy works via a single GLP-1 mechanism and may suit some individuals better than Mounjaro's dual mechanism. Some people respond better to one than the other. Your prescriber can assess whether a switch is appropriate based on your individual tolerability and response so far.
Can I skip doses to speed up Mounjaro's effect?
No — skipping doses or self-escalating is unsafe and ineffective. The titration schedule is carefully designed for safety and tolerability. Faster escalation increases side effects without improving results. Always follow your prescriber's schedule and discuss any concerns about pacing with them.
Why does Wegovy appear to work faster than Mounjaro?
It doesn't necessarily — both medications require titration. Wegovy has a longer safety history and more public awareness, so you may see more testimonials. SURMOUNT trial data actually showed Mounjaro achieved slightly higher average weight loss than Wegovy, but individual results vary. Your prescriber will recommend based on your suitability, not comparative trial averages.
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.