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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What Is The Active Ingredient In Mounjaro?
The active ingredient in Mounjaro is tirzepatide, a dual GIP and GLP-1 receptor agonist that works differently to other weight loss injections. If you're considering Mounjaro in the UK, understanding both the medication and how to access it is essential. This guide explains what tirzepatide is, how it works, and the practical steps to obtain a prescription through NHS or private routes, including current cost context for UK patients.
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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.
Understanding Tirzepatide and UK Access Routes
Tirzepatide is Mounjaro's active ingredient—a prescription-only medicine that activates two natural hormone pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual mechanism is what distinguishes Mounjaro from other weight loss injections like Wegovy, which only targets GLP-1. Tirzepatide may help regulate appetite, reduce food cravings, and support feeling fuller after meals. It comes as the Mounjaro KwikPen, a pre-filled injection device for once-weekly use.
In the UK, you can access Mounjaro through two main routes:
- NHS specialist services: Referral through your GP to a tier 3 or tier 4 weight management service. Availability and waiting times vary significantly by region and ICB (Integrated Care Board).
- Private prescribing: Online consultation with a UK-licensed prescriber, followed by prescription from a GPhC-registered pharmacy. This route does not require NHS referral.
Both routes require a clinical assessment to confirm eligibility based on BMI and health conditions.
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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.
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Everything you need to understand your weight, explore medication options, and track your progress — completely free.
UK Costs and What to Expect From Online Prescribing
Private Mounjaro costs in the UK typically range from £129 to £320 per month depending on the dose, with initial doses (2.5 mg) at the lower end and higher maintenance doses (15 mg) at the higher end. This is significantly more accessible than NHS waiting lists in many regions, though individual costs vary by provider. When you choose private prescribing, you'll complete an online health questionnaire with a UK-licensed prescriber who will assess your eligibility based on BMI, weight-related health conditions, and medication interactions. If approved, a prescription is issued to a registered pharmacy for dispensing. Always ensure the prescriber is registered with the GMC or equivalent regulatory body, and the pharmacy is GPhC-registered.
- 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 tirzepatide the same as Mounjaro?
Yes. Tirzepatide is the active pharmaceutical ingredient in Mounjaro. Mounjaro is the brand name, delivered as a pre-filled KwikPen injection. The terms are used interchangeably in medical practice.
How does tirzepatide differ from semaglutide in Wegovy?
Tirzepatide is a dual GIP and GLP-1 agonist, while semaglutide (Wegovy) is a GLP-1-only agonist. Clinical trials suggest tirzepatide may produce slightly greater average weight loss—around 15–21% body weight compared to Wegovy's ~15%—though individual results vary significantly.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro is NICE-approved for NHS use through specialist weight management services. However, NHS access requires referral from your GP and assessment by a tier 3 or tier 4 service. Availability and waiting times vary considerably by region.
What is the cost of Mounjaro with private prescribing in the UK?
Private Mounjaro typically costs £129–£320 per month depending on dose. Initial lower doses are cheaper. Prices vary between providers, so it's worth comparing GPhC-registered pharmacies. Always confirm the total cost upfront.
What happens during an online consultation for Mounjaro?
You'll complete a health questionnaire covering your BMI, weight-related conditions, current medications, and medical history. A UK-licensed prescriber reviews this, assesses eligibility, and if suitable, issues a prescription to a GPhC-registered pharmacy for dispensing. The process typically takes 24–48 hours.
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.