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 Am I Not Losing Weight On Mounjaro 5 Mg?
If you're on Mounjaro 5 mg and not seeing the weight loss results you expected, you're not alone. Weight loss on any prescription weight loss injection depends on multiple factors including dose, how long you've been taking it, diet, physical activity, and individual body response. This guide explains why progress may be slower than anticipated, how Mounjaro compares to Wegovy, and what steps to take next with your prescriber.
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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 5 Mg vs Wegovy: Trial Data and Mechanism
Mounjaro (tirzepatide) and Wegovy (semaglutide) are both weekly weight loss injections licensed in the UK, but they work differently. Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways. In the SURMOUNT-1 clinical trial, Mounjaro 5 mg produced an average weight loss of around 15% of body weight over 72 weeks. By comparison, Wegovy at its standard maintenance dose (2.4 mg) achieved approximately clinically studied weight loss in the STEP trials.
The key difference: Mounjaro's dual mechanism may help some patients lose more weight, but individual responses vary significantly. Mounjaro dose escalation is important — 5 mg is typically a starting or early maintenance dose. Many patients require escalation to 10 mg or 15 mg for optimal results. If you've just started at 5 mg or recently reached this dose, your body may still be adjusting, and your prescriber may recommend continuing for 4–8 weeks before considering a dose increase, depending on your response and tolerability.
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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.
Why Weight Loss May Be Slow: Key Factors
Dose and timing: 5 mg is often not the final maintenance dose. Clinical trials show greater weight loss at higher doses, so your prescriber may plan dose escalation over time.
Individual response: Some people respond more gradually to GLP-1 or GIP/GLP-1 therapy. This is not a failure — it reflects natural biological variation. Use our GLP-1 weight loss calculator to estimate realistic outcomes based on dose and individual factors.
Diet and activity: Mounjaro works best alongside a reduced-calorie diet and increased physical activity. Without these lifestyle changes, weight loss progress will be slower. Speak to your prescriber or a dietitian about your current habits.
How long you've been taking it: If you started recently, allow 4–8 weeks minimum to assess response at any given dose.
- 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 5 mg not working, or is it just a starting dose?
Mounjaro 5 mg is typically a starting or early dose used during the first 4 weeks of treatment. Most patients require escalation to 10 mg, 15 mg, or higher for significant weight loss. If you're on 5 mg, discuss with your prescriber whether dose escalation is planned and when to expect a review.
Could Wegovy be better than Mounjaro if I'm not losing weight?
Not necessarily. Wegovy and Mounjaro have similar average weight loss outcomes across trials, but individual response varies. Some people respond better to one medication over the other. Only your prescriber can advise whether a switch is appropriate based on your specific health profile and response so far.
How long should I stay on Mounjaro 5 mg before expecting results?
Allow at least 4–8 weeks at any given dose to assess response. Most patients take 16–20 weeks of dose escalation (starting at 2.5 mg, increasing every 4 weeks) before reaching their target maintenance dose. Weight loss typically accelerates as dose increases.
What if I'm following the diet and exercising but still not losing weight?
Speak to your prescriber. Factors like thyroid function, other medications, underlying health conditions, and genetics can affect weight loss. Your GP or specialist may recommend investigation or a prescriber reassessment to confirm the medication is right for you.
Could I lose more weight if I switched to Wegovy?
Maybe, but both medications have similar average trial outcomes (14–clinically studied weight loss). A switch would only be appropriate if your prescriber believes you've not responded adequately to Mounjaro at an optimised dose. This is an individual clinical decision, not a assured improvement.
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.