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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What to Do If Mounjaro 2.5mg Isn't Working
If you've been taking Mounjaro 2.5mg and haven't noticed weight loss, it's important to understand that this is the starting dose and you may need dose escalation. Weight loss medications work differently for different people, and individual results vary significantly. This guide explains when to expect results, how Mounjaro compares to Wegovy, and what your next steps should be with your prescriber. The starting dose is deliberately low to help your body adjust and minimise side effects—not to deliver maximum weight loss results.
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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 Starting Dose vs Full Dose: SURMOUNT Trial Context
Mounjaro 2.5mg is a starter dose only. In the SURMOUNT-1 clinical trial, participants on the starting dose of 2.5mg did not achieve significant weight loss compared to placebo. Meaningful weight loss typically began at 5mg and above, with average weight loss of approximately 15% at 5mg, rising to 20.9% at the maximum 15mg dose over 72 weeks.
Dose titration follows a strict schedule: you stay on 2.5mg for 4 weeks minimum, then increase to 5mg for weeks 5–8, continuing escalation every 4 weeks if needed and tolerated. This gradual approach is intentional—it allows your body to adapt and helps manage side effects like nausea. Use our GLP-1 weight loss calculator to explore potential outcomes at different doses to understand what to expect as you progress.
- Week 1–4: 2.5mg (adjustment phase, minimal weight loss expected)
- Week 5–8: 5mg (weight loss typically becomes noticeable)
- Week 9+: Escalation continues based on tolerability and response
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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.
Mounjaro vs Wegovy: Which Works Better If One Isn't Working?
Comparing Mounjaro and Wegovy directly is complex because they use different mechanisms. Mounjaro is a dual GIP+GLP-1 agonist, activating two hormone pathways, whilst Wegovy is a GLP-1-only agonist. In clinical trials, Mounjaro showed slightly higher average weight loss (up to 20.9%) than Wegovy (approximately 14.9%), but individual responses vary—some people respond better to one than the other.
If Mounjaro 2.5mg isn't working after proper dose escalation, switching to Wegovy is possible, though this requires a prescriber decision. Neither medication is assured to work for every person. Your prescriber may also consider whether you've reached an adequate dose or whether lifestyle factors (diet, activity, adherence) need reassessment before switching. A tirzepatide UK prescription requires ongoing clinical monitoring, so discuss response and options with your GP or prescriber.
Before considering a switch, ensure you've given Mounjaro adequate time at therapeutic doses. Most guidelines recommend staying at each dose for at least 4 weeks. If you're still on 2.5mg, you haven't yet reached the dose where clinical trial results were seen. Side effects like nausea often improve after 1–2 weeks on each dose, so early tolerability issues don't mean the medication won't work.
If you've progressed to 5mg or higher and experienced no weight loss after 12+ weeks, or if you've had significant side effects preventing dose escalation, your prescriber may consider alternatives. This is an individual decision based on your health, tolerance, and preferences. Use our BMI calculator to track your baseline and any changes over time, and keep detailed records to discuss with your healthcare provider.
- 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.
How long does it take for Mounjaro 2.5mg to work?
Mounjaro 2.5mg is the starting dose and typically does not produce noticeable weight loss. It's designed for dose adjustment and tolerance. Meaningful weight loss usually begins at 5mg and above. Most people need 4–8 weeks at a therapeutic dose (5mg+) to see results, though this varies. Keep a record of your progress.
Should I switch from Mounjaro to Wegovy if Mounjaro isn't working?
Not immediately. First, ensure you've escalated to adequate doses (5mg minimum) and given it sufficient time. If you have escalated and seen no response after 12+ weeks, discuss switching with your prescriber. Both medications work differently; some people respond better to one than the other. A switch requires a new clinical assessment.
What's the difference between Mounjaro and Wegovy mechanisms?
Mounjaro (tirzepatide) is a dual GIP+GLP-1 receptor agonist, activating two hormone pathways. Wegovy (semaglutide) is a GLP-1-only agonist. The dual mechanism may explain slightly higher average weight loss with Mounjaro in trials, but individual responses vary. Neither mechanism assures results for every person.
Can I skip doses to try again at 2.5mg if I don't like side effects?
No. Skipping doses or restarting at a lower dose can be unsafe and may cause blood sugar instability if you have diabetes. If side effects are intolerable, speak to your prescriber about slowing escalation or managing symptoms. Never adjust dosing without clinical guidance—your KwikPen is prescribed specifically for you.
What if I'm on 2.5mg Mounjaro and not losing weight—is it not working?
Not necessarily. At 2.5mg, weight loss is not expected; it's a starting dose. The dose is designed to help your body adjust, not to deliver maximum results. Once you escalate to 5mg (week 5) and beyond, weight loss typically becomes measurable. Patience with dose titration is essential. Track your baseline weight now using our progress tracker.
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.