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 Your 5mg Mounjaro May Not Be Working Yet
If you've been taking Mounjaro 5mg and haven't noticed weight loss, you're not alone — and it doesn't necessarily mean the medication isn't working for you. Many people find that the starting and early maintenance doses take time to show results. Understanding what to expect during the first weeks of treatment, and knowing when a dose increase might be appropriate, is crucial for managing your expectations and getting the most from your prescription. This guide covers the reasons you may not be seeing results at 5mg, realistic timelines, and what your prescriber might recommend next.
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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.
Understanding Mounjaro Dose Escalation and Timeline
Mounjaro is prescribed in a step-wise dose titration schedule, starting at 2.5mg and increasing every 4 weeks. The 5mg dose is typically used for weeks 5–8, meaning you've only been on it for up to 4 weeks. Your body needs time to adjust to each dose level, and weight loss often becomes more noticeable at higher doses. Clinical trial data (SURMOUNT-1) showed that participants on Mounjaro 5mg lost an average of around 15% of their body weight — but this was over 72 weeks, not the first month. Key reasons you may not see results yet include: you're still in the early escalation phase, your body is still adjusting to the medication's effects, you may need to progress to 7.5mg or higher for more significant results, and sustained weight loss takes time. If you've been on 5mg for 4 weeks and your prescriber hasn't scheduled a dose increase, ask whether you're due to escalate to 7.5mg at your next appointment. Weight loss medications work best when combined with reduced-calorie diet and increased physical activity — if lifestyle hasn't changed, results will be limited.
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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 Check Before Assuming It's Not Working
Before concluding Mounjaro 5mg isn't working, review these factors: Are you measuring results correctly? Weight fluctuates daily due to water retention, food volume, and hormonal changes — weigh yourself once per week at the same time, or use our free progress tracker to spot trends over weeks, not days. Have you made dietary changes? Mounjaro reduces appetite but doesn't create weight loss without a calorie deficit — if food intake hasn't decreased, weight may not change. Is your prescriber aware of any other medications? Some drugs (like oral contraceptives) have reduced absorption with Mounjaro and may affect outcomes. Do you have any underlying health conditions? PCOS, hypothyroidism, and other conditions can slow weight loss. Discuss these honestly with your GP or prescriber. If you're confident you've made lifestyle changes and still see no change after 4 weeks on 5mg, your next dose increase is likely due soon — this is when most people notice results.
- 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 should I wait on 5mg Mounjaro before concluding it's not working?
You should remain on 5mg for at least 4 weeks before assessing results, as this is the standard dose titration period. Weight loss typically becomes more noticeable at 7.5mg and higher. If you've been on 5mg for exactly 4 weeks, you're likely due for a dose increase — discuss timing with your prescriber. Individual results vary, and some people see modest results at lower doses.
What's the difference between Mounjaro and Wegovy for weight loss?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro starts at 2.5mg and goes up to 15mg weekly, whereas Wegovy starts at 0.25mg and maxes at 2.4mg. In clinical trials, Mounjaro showed slightly higher average weight loss — around 15–21% body weight compared to Wegovy's approximately 15% — but individual results vary greatly.
Could a lower dose be the reason I'm not losing weight?
Yes. The 5mg dose is a maintenance dose for weeks 5–8, not the therapeutic maximum. Most people see more significant results once they reach 7.5mg, 10mg, or higher. Your prescriber will increase your dose every 4 weeks if tolerated. If you've taken 5mg for a full month with no dietary changes, weight loss should increase after your next escalation.
Should I ask my prescriber to skip 5mg and go straight to a higher dose?
No. Dose escalation is designed to minimise side effects and allow your body to adjust gradually. Skipping doses can increase nausea, diarrhoea, and other gastrointestinal side effects. Stick to the prescribed schedule — the benefits become clearer once you reach your therapeutic dose, typically 10–15mg.
Can I use the BMI calculator to track my progress on Mounjaro?
Yes. Our free BMI calculator lets you enter your current weight and height to see your BMI instantly. Combined with our weight loss calculator and progress tracker, these tools help you monitor changes over weeks and months, showing trends that daily scales may not reveal. Tracking BMI alongside weight loss is especially useful on Mounjaro.
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.