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
Free tracker included with every download this week
Why Mounjaro May Not Be Causing Weight Loss
Not everyone loses weight on Mounjaro, and that's important to understand. Individual results vary significantly, and some people experience minimal weight loss despite taking the medication correctly. This guide explains why weight loss outcomes differ, what factors affect results, and how to access Mounjaro in the UK through NHS or private routes. We'll also help you understand the costs involved so you can make an informed decision about whether this weekly weight loss injection is right for your situation.
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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 Why Mounjaro Results Vary
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist that helped participants lose an average of 15–21% of their body weight in clinical trials — but "average" is key. Some people lose significantly more; others lose very little. Several factors influence individual outcomes. Genetics play a major role; some people's bodies respond more effectively to GIP/GLP-1 signalling than others. Adherence matters enormously: missing doses, not maintaining a reduced-calorie diet, or not increasing physical activity can substantially limit weight loss. Dose may also matter — you may need to reach a higher maintenance dose (10–15 mg) to see results, and dose titration takes months. Medical conditions like type 2 diabetes, insulin resistance, or thyroid disorders can affect weight loss. Additionally, some people plateau after initial weight loss, which is normal — the body adapts to medication over time. If you've been on Mounjaro for fewer than 12–16 weeks, results may still be developing.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
UK Access Routes: NHS vs Private & What It Costs
In the UK, there are two main routes to Mounjaro: NHS specialist services and private prescription. NHS access is through tier 3 or 4 specialist weight management services — typically requiring a GP referral. NICE has approved tirzepatide for NHS use, but availability and waiting lists vary dramatically by region (ICB). Some areas have waiting lists of 6–12 months or longer; others may not offer it at all. Private access is faster: an online consultation with a UK-licensed prescriber, followed by prescription through a GPhC-registered pharmacy. Private costs typically range from £129–£320 per month depending on your dose, with higher doses (15 mg) at the upper end. NHS costs are covered by the service if you're accepted. Neither route assures weight loss — both require a clinical assessment confirming you meet eligibility criteria (BMI ≥30, or ≥27 with weight-related health conditions).
- 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.
If I'm not losing weight on Mounjaro, should I increase my dose?
Not without guidance from your prescriber. Increasing dose too quickly can worsen side effects without necessarily improving weight loss. If you've been stable on your current dose for 8+ weeks with minimal loss, discuss options with your prescriber — they may recommend staying longer at your dose, increasing gradually, or exploring whether the medication is right for you.
How long should I wait before deciding Mounjaro isn't working?
Allow at least 16–20 weeks (4–5 dose escalations) before drawing conclusions. Clinical trials showed meaningful weight loss taking weeks to develop. If you're only 4–6 weeks in, your dose may still be too low. However, if you've been at a stable dose for 12+ weeks with no weight loss and you're adhering perfectly, it may be time to reassess with your prescriber.
Does the NHS cover Mounjaro if I'm not losing weight?
NHS coverage depends on your individual assessment and local policy. If you've been prescribed Mounjaro through NHS services and aren't losing weight, discuss this with your specialist team — they may adjust your approach, continue treatment longer, or try an alternative. There's no automatic stopping point based on weight loss alone.
What's the difference between private Mounjaro costs and Wegovy costs in the UK?
Mounjaro and Wegovy (semaglutide) are separate medications with different pricing. Mounjaro typically costs £129–£320/month; Wegovy usually ranges £129–£250/month depending on dose. The weekly weight loss injection you choose affects cost. Use our GLP-1 weight loss calculator to explore potential outcomes before committing to either medication.
Can I switch from Mounjaro to another weight loss injection if it's not working?
Possibly, but only under prescriber guidance. Switching to Wegovy (semaglutide) or liraglutide (Saxenda) may work better for some people, as individual medication responses vary. Your prescriber will assess whether switching is appropriate based on your tolerance, side effects, and weight loss goals.
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.