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 7.5mg Mounjaro May Not Be Working
If you're on a 7.5mg dose of Mounjaro and haven't seen the weight loss results you expected, you're not alone — and there are several reasons this may be happening. Weight loss with tirzepatide varies significantly between individuals, and a slower response doesn't necessarily mean the medication isn't working. Understanding what affects results, and when to contact your prescriber, is essential. This guide explains the common reasons for slower weight loss on Mounjaro and what steps you can take next.
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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.
Common Reasons Weight Loss May Be Slower on Mounjaro
Several factors can affect how well Mounjaro works for you, even at the 7.5mg dose:
- Dietary adherence: Mounjaro reduces appetite and hunger, but you still need to maintain a calorie deficit. If you're eating at maintenance calories (the amount needed to stay at your current weight), weight loss will stall. Use our free BMI calculator and weight converter to track where you sit, and ensure you're genuinely in a deficit — ideally around 500 calories below your maintenance level for 0.5kg per week loss.
- Metabolism and genetics: Clinical trials showed Mounjaro helps participants lose an average of 15–21% of body weight, but individual results vary. Some people respond faster than others due to genetics, age, and metabolic rate.
- Dose timing: You're on 7.5mg, which is an escalation dose. Your body may still be adjusting. Mounjaro dose titration typically requires a minimum of 4 weeks at each dose level before increasing further — staying at 7.5mg for 4–8 weeks allows your system to fully adapt.
- Medication interactions: Mounjaro may affect how quickly your body absorbs other oral medications, and some medications can affect weight loss. Inform your prescriber of all medications you take.
- Insufficient physical activity: Weight loss injections work best alongside increased movement. Even modest activity — walking 30 minutes most days — significantly improves results.
- Water retention or recent gains: Short-term weight fluctuations are normal. Track progress over weeks, not days, using our free progress tracker to see the true trend.
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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 Delivering Results
Step 1: Give it more time. If you've only been at 7.5mg for 2–3 weeks, continue for the full 4-week adjustment period before drawing conclusions.
Step 2: Assess your diet honestly. Mounjaro suppresses appetite, but weight loss still requires eating fewer calories than you burn. Keep a food diary for 3–5 days to identify where calories may be creeping in — often through drinks, snacks, or portion sizes larger than expected.
Step 3: Contact your prescriber. If you've been on 7.5mg for 4+ weeks, eaten in a clear calorie deficit, increased activity, and seen no weight loss, speak to your GP or the prescriber who issued your Mounjaro KwikPen. They may recommend dose escalation to 10mg, or investigate other factors like thyroid function or medication interactions. Your prescriber can also confirm whether you're using the KwikPen correctly — improper injection technique can reduce effectiveness.
Step 4: Rule out other causes. Weight loss resistance can sometimes signal underlying thyroid issues, PCOS, or other medical conditions. Your GP can run blood tests if needed.
- 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 to see weight loss on 7.5mg Mounjaro?
Most people see initial weight loss within 2–4 weeks of reaching their therapeutic dose, but individual timescales vary. Some see changes at weeks 1–2, others may take 4–8 weeks. If no change after 4 weeks at 7.5mg with calorie deficit and activity, contact your prescriber about dose escalation to 10mg.
Should I increase my Mounjaro dose if it's not working?
Never increase your dose without consulting your prescriber. Mounjaro dose titration is controlled — you must stay at each dose level for a minimum of 4 weeks. Your prescriber will assess whether 10mg is appropriate based on your response, side effects, and overall health.
Does Mounjaro vs Wegovy make a difference if one isn't working?
Mounjaro (tirzepatide) and Wegovy (semaglutide) work differently. Mounjaro is a dual GIP + GLP-1 agonist; Wegovy is a GLP-1 agonist only. Some people respond better to one than the other. If Mounjaro isn't delivering results, your prescriber might discuss switching to Wegovy or another option, but this decision is individual and requires clinical assessment.
What if I'm not losing weight but feel full on Mounjaro?
Feeling full is a sign the medication is working — it's suppressing appetite as intended. Weight loss requires both appetite suppression AND a calorie deficit. You might not feel hungry, but if portions are still large, you may be eating too much. Use our BMI calculator and progress tracker to monitor actual weight change over 4–8 weeks, as appetite suppression is working even if the scales haven't moved yet.
Is Mounjaro not working, or am I not eating in a deficit?
This is the most common issue. Mounjaro doesn't clinically studied weight loss on its own — it reduces hunger, but you must eat fewer calories than you burn. Calculate your maintenance calories (roughly body weight in kg × 24–30, depending on activity), then aim for 500 calories less per day. If you're uncertain, ask your GP or a registered dietitian to review your diet. ```
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