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
Starting Mounjaro: What You Need to Know
Starting Mounjaro (tirzepatide) is a significant step in weight management for eligible UK adults. Mounjaro is a prescription-only, once-weekly injectable medication that works by activating natural hormone pathways to help regulate appetite and support weight loss alongside lifestyle changes. Before beginning treatment, you'll need a clinical assessment to ensure it's suitable for your health profile. This guide covers eligibility, how the starting dose works, what to expect in the first weeks, and how to access Mounjaro through NHS or private channels in the UK.
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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.
How to Access Mounjaro in the UK
NHS Route: You'll need referral from your GP to a tier 3 specialist weight management service. The service will assess your eligibility based on BMI and health conditions, then prescribe Mounjaro if appropriate. NHS availability varies significantly by region — some areas have long waiting lists. Use our free BMI calculator to check if you may meet the threshold (BMI 30+ or BMI 27–29.9 with weight-related health conditions).
Private Route: Online consultation with a UK-licensed prescriber, followed by prescription from a GPhC-registered pharmacy if clinically appropriate. No NHS referral needed. Available without waiting lists but involves private costs (typically £129–£320+ monthly depending on dose).
Assessment Requirements: Any prescriber will assess your medical history, current medications, kidney and liver function, and whether you have any contraindications. Be honest about all medications, supplements, and health conditions.
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.
Your First Mounjaro Dose and What to Expect
Your first Mounjaro dose is always 2.5 mg — a starting dose that your body adjusts to over 4 weeks. You'll inject once weekly using the pre-filled KwikPen. Side effects are common in the first few weeks (nausea, changes in appetite, mild stomach discomfort) and typically ease as your body adapts. Keep to your reduced-calorie diet and activity — Mounjaro works best alongside lifestyle changes, not instead of them.
After 4 weeks, your prescriber will discuss whether to increase to 5 mg. Dose increases happen every 4 weeks, stepping up to 7.5 mg, 10 mg, 12.5 mg, and finally 15 mg (maximum). Most people see weight loss results by week 8, though individual timelines vary. Try our free GLP-1 weight loss calculator to estimate potential outcomes at different doses.
- 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.
Do I need a prescription to start Mounjaro in the UK?
Yes, Mounjaro is prescription-only in the UK and requires a clinical assessment before being prescribed. You cannot buy it over the counter or without a prescription from a licensed UK prescriber. Assessment ensures it's safe and appropriate for your individual health profile.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials suggest Mounjaro may produce slightly higher average weight loss (~21% vs ~15%), but both are effective. Your prescriber will recommend based on your health and preferences.
How much weight will I lose starting Mounjaro?
Clinical trials (SURMOUNT-1) showed average weight loss of around 15% body weight at the 5 mg dose and up to 21% at maximum dose (15 mg) over 72 weeks — but individual results vary significantly. Weight loss also depends on diet, activity, and personal factors. Some people lose more, some less.
Can I start Mounjaro if I have type 2 diabetes?
Yes, you may be eligible. Having type 2 diabetes counts as a weight-related health condition under UK prescribing criteria, which can lower the BMI threshold for eligibility to 27–29.9. Your prescriber will assess whether Mounjaro is appropriate alongside your diabetes medication.
What happens if I get side effects when starting Mounjaro?
Nausea and stomach changes are very common in the first 2–4 weeks and usually ease as your body adjusts. Staying hydrated, eating smaller meals, and avoiding greasy foods helps. If side effects are severe or persist beyond 4 weeks, contact your prescriber — they may recommend staying at your current dose longer before increasing.
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.