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
What Is Mounjaro and How Does It Work?
Mounjaro is a prescription-only weight management injection containing tirzepatide, licensed for use in the UK. It's a dual GIP and GLP-1 receptor agonist — meaning it works on two natural hormone pathways to help reduce appetite and support weight loss alongside a reduced-calorie diet and increased physical activity. Understanding how Mounjaro works, who can access it through the NHS, and what to expect is essential before discussing this treatment with your GP or a healthcare professional.
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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.
How Mounjaro Works and NHS Eligibility in the UK
Mechanism of action: Mounjaro activates two hormone pathways — GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) — unlike single-action medications such as Wegovy. This dual mechanism helps regulate appetite, reduce food cravings, and support feeling fuller after smaller meals. It also slows gastric emptying (how quickly food leaves the stomach), though this effect typically reduces over time.
NHS eligibility: In the UK, Mounjaro may be prescribed on the NHS for adults with a BMI of 30 kg/m² or above, or a BMI of 27–29.9 kg/m² with weight-related health conditions such as type 2 diabetes, prediabetes, high blood pressure, or cardiovascular disease. For adults of South Asian, Chinese, Black African, or Black Caribbean backgrounds, lower BMI thresholds apply due to higher health risks at lower weights. Access is through specialist tier 3 weight management services — not standard GP prescription — and availability varies significantly across UK regions.
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.
Mounjaro Doses, Side Effects, and UK Access Routes
Mounjaro is available in weekly doses ranging from 2.5 mg (starting dose) to 15 mg (maximum maintenance dose). Common side effects include nausea, diarrhoea, vomiting, and constipation, particularly during dose escalation — these typically improve over time. Clinical trials showed that participants using the 15 mg maintenance dose lost an average of approximately 21% of their body weight over 72 weeks, though individual results vary significantly and depend on lifestyle changes.
In the UK, Mounjaro is available through two routes: NHS specialist weight management services (with long waiting lists in many regions) or private online prescribing following a clinical assessment with a UK-licensed prescriber. A prescriber will evaluate your personal health history, current medications, and suitability before issuing a prescription dispensed by a GPhC-registered pharmacy.
- 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.
Is Mounjaro the same as Wegovy?
No. Both are prescription weight loss injections available in the UK, but they work differently. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) activates GLP-1 only. Clinical trial data suggests Mounjaro may produce slightly greater weight loss on average, though individual results vary significantly.
Can I get Mounjaro through my NHS GP?
Mounjaro is not routinely prescribed by GPs. Access on the NHS is through specialist tier 3 weight management services — you'll need a GP referral. Waiting times vary by region; in many areas, lists are several months long. Private access is available through online prescribers without an NHS referral.
What is the Mounjaro KwikPen?
The Mounjaro KwikPen is the delivery device used to inject Mounjaro. Each pen contains four weekly doses (one month's supply) and is pre-filled. You store it in the fridge and inject once per week into your stomach, thigh, or upper arm. After 30 days of use, the pen is disposed of.
What dose of Mounjaro would I start on?
Everyone starts at 2.5 mg weekly, regardless of final maintenance dose. You remain on each dose for at least four weeks before increasing. Dose titration — the gradual increase in dose — continues until you reach your effective maintenance dose or reach the 15 mg maximum.
How much weight loss does Mounjaro actually produce?
In the SURMOUNT-1 clinical trial, participants lost an average of 15–21% of their body weight depending on dose (over 72 weeks alongside reduced-calorie diet and exercise). However, individual results vary significantly — some lose more, some less. Your personal outcome depends on genetics, adherence, diet, and activity levels.
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.