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 Am I Putting On Weight With Mounjaro?
Weight gain during Mounjaro treatment is unusual but can happen for several reasons. Some people experience weight regain after stopping the injection, whilst others may not lose weight at the expected rate. Understanding why this occurs and knowing your options — including accessing Mounjaro through NHS services or private prescriptions in the UK — can help you make informed decisions about your weight management journey. Our free GLP-1 weight loss calculator can help you understand expected outcomes at different doses.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Why Weight Gain Happens on Mounjaro — And Access Options in the UK
Weight gain or slower-than-expected weight loss on Mounjaro can occur for several reasons. Dose too low: If you're on a starting or low maintenance dose (2.5–5 mg), weight loss may be modest compared to higher doses (10–15 mg). Clinical trials showed average weight loss of 15% at 5 mg but 20.9% at 15 mg — dose significantly affects outcomes. Lifestyle factors: Mounjaro works alongside reduced-calorie diet and physical activity. Without dietary changes, weight loss plateaus. Individual variation: Some people respond differently to GLP-1 medication; genetics, metabolism, and other medical conditions play a role. Medication interactions: Certain medicines can affect weight loss outcomes. Stopping treatment: Weight often returns within months of stopping — Mounjaro maintains weight loss only whilst taking it. Your GP or prescriber can review your dose, diet, and other factors if progress stalls. If you're not seeing results after 12 weeks on an adequate dose, discussing dose escalation or alternative options is important.
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.
Accessing Mounjaro in the UK — NHS and Private Routes
NHS access: Mounjaro is approved by NICE for specialist weight management services in the UK. You'll typically need a GP referral to a tier 3 or tier 4 specialist weight management service. Availability varies by region; waiting lists can be several months or longer in many areas. Once approved, the NHS covers the cost of the medication itself. Private access: Available through GPhC-registered online prescribing services without NHS referral. An online clinical assessment with a UK-licensed prescriber determines suitability. If approved, prescriptions are dispensed by licensed pharmacies. Private costs typically range from £129–£320 per month depending on dose — higher doses cost more. Private access is faster but you pay the full cost. Your choice depends on urgency, regional NHS availability, and budget. Use our free BMI calculator to confirm your eligibility (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.
Can Mounjaro cause weight gain?
Weight gain on Mounjaro is uncommon but can happen if your dose is too low, you've not changed your diet, or you have underlying medical conditions affecting weight loss. Individual variation is significant. If you're gaining weight or not losing as expected, discuss dose adjustment with your prescriber — escalating from 5 mg to 10 mg or 15 mg often improves results.
What does Mounjaro cost on the NHS in the UK?
Mounjaro is free on the NHS if prescribed through a specialist weight management service following a clinical assessment. However, NHS access requires a GP referral and availability varies significantly by region — waiting times can be several months in many areas.
How much does private Mounjaro cost in the UK?
Private Mounjaro typically costs £129–£320 per month depending on dose. Doses 2.5–5 mg are cheaper; higher doses (10–15 mg) cost more. Prices vary between GPhC-registered prescribing services. You'll also pay for the initial online consultation (usually £30–£50). Always confirm the total cost before starting.
How long does it take to access Mounjaro privately in the UK?
Private access is much faster than NHS. Most online consultations take 24–48 hours for assessment. If approved, your prescription is issued immediately and typically dispensed within 2–5 working days. You could receive your first KwikPen within a week, compared to NHS waiting lists of months.
Do I need a prescription for Mounjaro in the UK?
Yes, Mounjaro is prescription-only in the UK. It's only available following a clinical assessment by a licensed UK prescriber — either through your GP/NHS specialist service or through a private online prescribing service. You cannot buy it without a valid 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.