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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Gaining Weight on Mounjaro — Understanding Weight Changes and UK Access
Some people experience weight gain on Mounjaro despite it being a weight loss injection. This can happen for several reasons — appetite returning as your body adapts, dose changes, lifestyle factors, or individual response variation. Understanding why this occurs and knowing how to access Mounjaro in the UK — whether through the NHS or private prescription — can help you make informed decisions about your treatment and next steps. This guide covers both the clinical context and the practical access routes available to UK adults.
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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.
Why Weight Gain Can Happen on Mounjaro — And UK Access Routes
Weight gain on Mounjaro can occur for several reasons. As your body adapts to the medication over weeks or months, appetite suppression may gradually reduce — this is particularly common if you're not increasing your dose as recommended. Some individuals also find that once initial weight loss plateaus, lifestyle habits may drift if dietary discipline isn't maintained. Additionally, certain medical conditions (thyroid issues, hormonal changes) or other medications can interfere with weight management outcomes. Importantly, individual response to GLP-1 medications varies significantly — what works well for one person may be less effective for another. If you're gaining weight on Mounjaro, discussing this with your prescriber is essential. They may recommend dose escalation, lifestyle review, or exploring alternatives like a weekly weight loss injection such as Wegovy, which uses a different mechanism. Access in the UK depends on your route: NHS specialist services (longer wait times, no direct cost) or private prescription (faster access, out-of-pocket cost).
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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.
NHS vs Private Access — How to Get Mounjaro in the UK
NHS route: Mounjaro is available through tier 3 specialist weight management services, but access requires a GP referral and is subject to regional availability and waiting lists — some areas have waits of 12 months or longer. Once prescribed through the NHS, there is no direct cost to you. Private route: You can obtain a Mounjaro UK prescription through a GPhC-registered online pharmacy following a clinical assessment with a UK-licensed prescriber — no NHS referral needed. This typically takes 24–48 hours. Costs vary by dose but generally range from £140–£320 per month. To access privately, you'll complete an online health questionnaire, have a brief clinical consultation, and if approved, your prescription is sent to a pharmacy for dispensing. Both routes require a clinical assessment to confirm eligibility and suitability.
- 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.
Why am I gaining weight on Mounjaro if it's supposed to help with weight loss?
Weight gain on Mounjaro can happen due to appetite returning as your body adapts, not escalating your dose as planned, lifestyle drift, or individual variation in response. Some people also have underlying medical conditions that affect weight. Discuss this with your prescriber — they may adjust your dose, review your diet, or explore alternatives.
What's the cost difference between NHS and private Mounjaro in the UK?
NHS Mounjaro is free at point of use, but requires a GP referral and can involve long waiting lists. Private Mounjaro costs approximately £140–£320 per month depending on your dose, but offers faster access (24–48 hours) without a referral. Calculate your potential outcomes using our free GLP-1 weight loss calculator.
How quickly can I get a private Mounjaro prescription in the UK?
Private prescription routes typically take 24–48 hours from online consultation to dispensing. You'll complete a health questionnaire, have a brief video or phone assessment with a UK-licensed prescriber, and if approved, your prescription is sent to a GPhC-registered pharmacy for immediate dispatch.
What's the difference between Mounjaro and Wegovy for weight management?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 injection; Wegovy (semaglutide) is a GLP-1-only injection. Clinical trials showed Mounjaro achieved slightly higher average weight loss (~21% vs ~15%), but individual results vary. Both are once-weekly injections available privately in the UK, though costs and dose ranges differ.
Will my GP prescribe Mounjaro privately if NHS waiting lists are too long?
Most GPs cannot prescribe Mounjaro for private use — weight management medication prescribing is typically restricted to NHS tier 3 services or private online prescribers. You'll need to access private Mounjaro through a private prescription service following a separate clinical assessment, not through your GP.
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.