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 Isn't My 7.5mg Mounjaro Working?
If you're on 7.5mg Mounjaro and haven't noticed weight loss, you're not alone—individual results vary significantly, and several factors affect how well the medication works for you. Weight loss doesn't always happen at the same pace for everyone, even at the same dose. This guide explains what might be happening, when to expect results, and what to discuss with your prescriber. Remember, Mounjaro (tirzepatide) is a prescription-only medicine, and your treatment should always be monitored by a healthcare professional who knows your full health picture.
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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.
Common Reasons Mounjaro May Not Be Delivering Results Yet
Timing matters: At 7.5mg, you're still in the dose titration phase. The clinical trials showed weight loss built up over time—most significant changes appeared after 12–16 weeks at your current dose. If you've only been on 7.5mg for a few weeks, your body may still be adjusting. Your prescriber may recommend staying at this dose for a minimum of 4 weeks before increasing further.
- Lifestyle factors: Mounjaro works alongside a reduced-calorie diet and increased physical activity—without these, results are limited. If your calorie intake has drifted upward or exercise has reduced, this directly impacts weight loss.
- Individual metabolism: Genetic factors, age, muscle mass, and baseline health all affect how quickly weight loss occurs. Some people respond faster at lower doses; others need higher doses.
- Underlying health conditions: Thyroid disorders, polycystic ovary syndrome (PCOS), type 2 diabetes, and cortisol issues can slow weight loss independent of the medication.
- Medication interactions: Certain medications (particularly some antipsychotics and corticosteroids) can interfere with weight loss. Review all medications with your prescriber.
Use our free GLP-1 weight loss calculator to compare your progress against typical trial outcomes—this can help you see whether you're on track for your dose level.
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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.
When to Speak with Your Prescriber
If you've been on 7.5mg Mounjaro for at least 4 weeks and have noticed no weight loss whatsoever, or if you've experienced significant side effects preventing you from eating less, contact your prescriber. They may:
- Increase your dose to 10mg (the next step in titration)
- Review your diet and activity level to identify barriers
- Check for underlying health conditions affecting weight loss
- Discuss whether Mounjaro is the right fit for you, or whether switching to an alternative like Wegovy might be considered
- Assess whether you're following injection technique correctly—improper injection won't deliver the full dose
Be honest about diet, exercise, and any challenges you're facing. Your prescriber can only help if they have complete information. Weight loss is a journey, not a race.
- 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 7.5mg Mounjaro take to work?
Most people need at least 4–8 weeks at any given dose to assess whether it's working. Clinical trials showed progressive weight loss over 16+ weeks. If you've been on 7.5mg for less than 4 weeks, your body is still adjusting. Your prescriber can advise whether to wait or escalate to the next dose.
Is 7.5mg a low dose of Mounjaro?
Yes. The Mounjaro KwikPen dose range runs from 2.5mg to 15mg weekly. At 7.5mg, you're in the mid-range during titration. Many people eventually increase to 10mg, 12.5mg, or 15mg depending on response and tolerability.
Should I switch from Mounjaro to Wegovy if it's not working?
This is a decision for your prescriber. Mounjaro is a dual GIP+GLP-1 agonist (two mechanisms), while Wegovy (semaglutide) is GLP-1 only. Clinical trial data shows both can support weight loss, but individual response varies. Your prescriber can discuss whether switching makes sense based on your specific situation and any side effects.
What if I'm not following the injection technique correctly?
Incorrect technique (wrong angle, not holding the button long enough, injecting into the same spot repeatedly) can reduce how much medication enters your system. Review the instruction leaflet, watch the Mounjaro KwikPen demonstration video provided by your pharmacy, or ask your pharmacist to show you the correct technique at your next visit.
Can I combine Mounjaro with other weight loss methods?
Always ask your prescriber before adding anything—other medications, supplements, or extreme diets. Mounjaro is designed to work with a balanced, reduced-calorie diet and regular activity. Very restrictive diets can cause nutrient deficiencies. Your GP or specialist can advise on safe combinations that complement your prescription.
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.