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 in Mounjaro — Active Ingredient & How It Works
Mounjaro contains tirzepatide, a dual GLP-1 and GIP receptor agonist that works differently from other weight loss injections available in the UK. This prescription-only medicine is injected once weekly and works by activating two natural hormone pathways that help regulate appetite and blood sugar. Understanding what's in Mounjaro and how it functions can help you make an informed decision about whether this medication might be suitable for you alongside a reduced-calorie diet and increased physical activity.
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.
The Active Ingredient: Tirzepatide Explained
Tirzepatide is the active pharmaceutical ingredient in Mounjaro, manufactured by Eli Lilly and Company. Unlike standard GLP-1 receptor agonist injections, tirzepatide is unique because it activates two hormone pathways simultaneously: GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide). This dual mechanism may help explain why clinical trials showed average weight loss of approximately 15–21% of body weight over 72 weeks, though individual results vary significantly.
The tirzepatide in Mounjaro helps regulate appetite by signalling to your brain that you feel fuller after eating smaller portions. It also slows how quickly food leaves your stomach and supports better blood sugar control. The medication comes as a once-weekly injection using a convenient pre-filled KwikPen device. Doses range from 2.5 mg (starting dose) up to 15 mg (maximum dose), with each dose escalated gradually over weeks to minimise side effects.
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 and Prescription Routes
In the UK, Mounjaro is prescription-only and requires a clinical assessment before being prescribed. Access is available through two main routes: NHS specialist weight management services (tier 3/4) via GP referral, though waiting lists can be lengthy in many areas, and private online prescribing services registered with the GPhC (General Pharmaceutical Council).
Private online consultations typically cost £15–£50 and involve answering health questions assessed by a UK-licensed prescriber. If approved, the prescription is dispensed by a registered online pharmacy. Monthly costs for Mounjaro vary by dose (approximately £129–£320) but are significantly lower than many overseas options. You can use our free GLP-1 weight loss calculator to explore projected results at different doses, and our BMI calculator to establish your baseline before starting treatment.
In the UK, Mounjaro is prescription-only and requires a clinical assessment before being prescribed. Access is available through two main routes: NHS specialist weight management services (tier 3/4) via GP referral, though waiting lists can be lengthy in many areas, and private online prescribing services registered with the GPhC (General Pharmaceutical Council).
Private online consultations typically cost £15–£50 and involve answering health questions assessed by a UK-licensed prescriber. If approved, the prescription is dispensed by a registered online pharmacy. Monthly costs for Mounjaro vary by dose (approximately £129–£320) but are significantly lower than many overseas options. You can use our free GLP-1 weight loss calculator to explore projected results at different doses, and our BMI calculator to establish your baseline before starting treatment.
- 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.
What exactly is tirzepatide and how is it different from other weight loss injections?
Tirzepatide is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways unlike standard GLP-1-only injections. This dual mechanism may support greater appetite reduction and blood sugar control. Clinical trials showed average weight loss of 15–21% of body weight with tirzepatide, compared to approximately 15% with GLP-1-only medications, though individual results vary significantly.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs typically range from £129–£320 per month depending on dose strength, with starting doses costing less than maximum doses. This includes the prescription assessment (usually £15–£50) plus the medication itself from a registered GPhC pharmacy. NHS access is free but often involves lengthy waiting lists for specialist weight management services.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro is available through NHS specialist weight management services (tier 3/4), but access requires a GP referral and assessment by a specialist team. Availability and waiting times vary significantly by region. Many areas have waiting lists of several months. Private online prescribing offers faster access but involves out-of-pocket costs.
What happens during a private online consultation for Mounjaro?
You'll complete an online health questionnaire covering your medical history, current medications, and weight loss goals. A UK-licensed prescriber reviews your answers to assess suitability. If approved, a prescription is issued to a registered pharmacy for dispensing. The entire process typically takes 24–48 hours from consultation to prescription approval.
Is tirzepatide the same as the medication in Wegovy or Saxenda?
No. Mounjaro contains tirzepatide (a dual GIP+GLP-1 agonist), while Wegovy contains semaglutide (GLP-1 only) and Saxenda contains liraglutide (GLP-1 only). Tirzepatide's dual mechanism may offer different efficacy, though clinical comparison studies are ongoing. All three are prescription-only weight management medications licensed in the UK.
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.