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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Your Mounjaro Journey in the UK
Starting a Mounjaro journey involves understanding how tirzepatide works, whether you're eligible through NHS services, and what the prescription and treatment process looks like in the UK. Mounjaro is a once-weekly injection licensed for weight management in adults, and your journey may begin through either NHS specialist services or private prescribing. This guide covers eligibility criteria, the dose titration schedule, what to expect at each stage, and how the NHS NICE pathway works compared to private access.
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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.
NHS Eligibility and the UK Prescription Pathway
Your Mounjaro journey in the UK typically starts with assessment of your eligibility. According to NHS and NICE guidance, you may qualify if you have a BMI of 30 kg/m² or above, or a BMI of 27–29.9 with a weight-related health condition such as type 2 diabetes, high blood pressure, sleep apnoea, or cardiovascular disease. If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply — eligibility may start at BMI 27.5 or above.
NHS access is through tier 3 specialist weight management services, usually reached via GP referral. However, NHS availability varies significantly by region and waiting lists can be lengthy. Your GP can advise whether your local integrated care board (ICB) currently commissions tirzepatide and what the wait time is. Private prescribing offers faster access — you can begin your Mounjaro journey within days following an online clinical assessment with a UK-licensed prescriber.
- NHS route: GP referral → specialist assessment → prescription at tier 3 service
- Private route: Online consultation → clinical assessment → prescription issued
- Ethnicity-adjusted thresholds apply for South Asian and Black African/Caribbean adults
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.
Dose Titration and What to Expect on Your Mounjaro Journey
Your Mounjaro journey follows a structured dose titration schedule, starting at 2.5 mg and escalating every 4 weeks if tolerated. Week 1–4 you take 2.5 mg, weeks 5–8 you increase to 5 mg, and your prescriber may continue escalating you through 7.5 mg, 10 mg, 12.5 mg, and finally 15 mg depending on your response and side effects. Most people reach an effective maintenance dose between 5–10 mg. Use our free GLP-1 weight loss calculator to estimate potential weight loss at different doses based on clinical trial data — individual results vary significantly. Common side effects during your journey include nausea, diarrhoea, and constipation, typically mild and improving as your body adjusts. Keep your prescriber informed of any persistent side effects.
- 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.
How long does a typical Mounjaro journey take in the UK?
The full dose escalation schedule takes approximately 20 weeks (from 2.5 mg to maximum 15 mg, increasing every 4 weeks). However, many people reach an effective dose at 5–10 mg, which takes 8–12 weeks. Weight loss typically becomes noticeable after 4–8 weeks on an effective dose. The overall journey from initial assessment to meaningful results may take 3–6 months depending on NHS waiting times.
Can I switch from Wegovy to Mounjaro on my NHS journey?
Yes, but it requires your prescriber's approval. Mounjaro is a dual GIP and GLP-1 agonist, whereas Wegovy (semaglutide) is GLP-1 only, so they work slightly differently. If you're currently on Wegovy and wish to switch, discuss this with your GP or specialist — they may restart you at 2.5 mg Mounjaro or use an approximate dose conversion. Any switch must be managed medically, never done independently.
What happens to my Mounjaro journey if I experience side effects?
Common side effects like nausea and diarrhoea often improve within 1–2 weeks as your body adjusts. If they persist, your prescriber may delay your next dose increase, keep you on your current dose longer, or suggest strategies like eating smaller meals or adjusting diet. Serious side effects (severe stomach pain, allergic reactions, changes in vision) require immediate medical attention. Your journey may be paused or stopped if side effects outweigh benefits.
How do I track progress on my Mounjaro journey?
The best way is regular weight monitoring — aim for weekly or fortnightly weigh-ins to see patterns. Our free progress tracker helps you log weight changes, energy levels, and how clothes fit over time. Your prescriber will also monitor your weight at appointments. Clinical trials showed tirzepatide helped participants lose 15–21% body weight on average, though individual results vary. Track your BMI alongside weight using our free BMI calculator to understand both metrics.
What's the difference between my Mounjaro journey on the NHS versus privately?
NHS route involves specialist assessment, longer waiting times (potentially months), and treatment as part of a comprehensive weight management programme. Private route is faster (days to weeks), more flexible with dose adjustments, and you choose your prescriber — but you pay directly, typically £150–£300 per month depending on dose. Both require prescription and clinical assessment; both use the same medication and dose schedule.
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.