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
When Will Mounjaro Start Working in the UK?
Mounjaro (tirzepatide) typically begins showing effects within the first few weeks, though individual results vary significantly. Most people notice appetite suppression and reduced food cravings within 2–4 weeks of starting the 2.5 mg dose. However, meaningful weight loss usually becomes visible around 4–8 weeks as your body adjusts to the medication. Full effects at each dose level take approximately 4 weeks to develop, which is why prescribers wait at least 4 weeks before increasing your dose. Access to Mounjaro in the UK depends on whether you pursue NHS or private routes, each with different timelines and costs.
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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.
Mounjaro Dose Titration and Timeline for Results
Mounjaro works through dose titration — gradual dose increases over weeks to minimise side effects and allow your body to adapt. Here's the typical timeline:
- Weeks 1–4: Start on 2.5 mg. Most people experience initial nausea, reduced appetite, and early appetite suppression during this phase.
- Weeks 5–8: Increase to 5 mg. Side effects often improve as your body adapts. Weight loss typically becomes noticeable by week 6–8.
- Weeks 9–12+: Further dose escalation (7.5 mg, 10 mg, etc.) if needed. Results continue to improve over subsequent weeks.
Clinical trials showed that patients achieved meaningful weight loss averaging 15–21% of body weight over 72 weeks on Mounjaro when combined with reduced-calorie diet and increased physical activity. The dual GIP and GLP-1 mechanism means effects build gradually rather than happening overnight. Individual response varies — some people see results faster, others require higher doses to notice change. Your prescriber will monitor your progress and adjust your dose schedule accordingly.
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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.
How to Access Mounjaro in the UK: NHS vs Private
NHS access: Mounjaro is available through specialist tier 3 and 4 weight management services, but access varies significantly by region. Your GP can refer you, though waiting lists can be months to years in some areas. NHS prescribing is covered by the health service once you're in the specialist pathway.
Private access: You can obtain Mounjaro through UK-licensed prescribers via online consultation without NHS referral. The process typically takes 24–48 hours from consultation to prescription. A GPhC-registered pharmacy then dispenses your KwikPen. Private Mounjaro costs range from approximately £129–£280 per month depending on your dose. Our GLP-1 weight loss calculator can help you estimate potential outcomes at different doses, and our BMI calculator shows where you sit relative to NHS eligibility thresholds.
- 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 it take to feel Mounjaro working?
Most people notice reduced appetite and food cravings within 2–4 weeks of starting the 2.5 mg dose. Visible weight loss typically appears around 4–8 weeks. Full effects at each dose level take about 4 weeks, which is why prescribers wait 4 weeks minimum before dose increases. Results vary — some people experience faster changes, others progress more slowly.
Can I access Mounjaro on the NHS in the UK?
Yes, Mounjaro is NICE-approved for NHS use through specialist weight management services (tier 3/4). However, availability depends on your regional NHS trust (ICB). Your GP can refer you, but waiting lists vary from months to over a year in some areas. Private access via online prescription is faster but involves personal cost.
What does Mounjaro cost privately in the UK?
Private Mounjaro costs approximately £129–£280 per month depending on your dose. A full month's supply is one KwikPen containing 4 weekly injections. Prices vary slightly between providers. Some offer starter packages or monthly subscriptions. Always check whether the price includes the clinical assessment consultation.
What's the difference between Mounjaro and Wegovy for timeline and cost?
Both are once-weekly injections. Mounjaro (tirzepatide) uses a dual GIP+GLP-1 mechanism and may show effects slightly faster in clinical trials compared to Wegovy (semaglutide, GLP-1 only). Privately, Mounjaro and Wegovy cost similarly (£129–£280/month), though pricing varies by provider. NHS access criteria are the same for both.
What happens if Mounjaro doesn't work for me after several weeks?
If you're not seeing expected results after 8–12 weeks, your prescriber will assess whether your dose needs increasing, whether the medication is suitable for you, or whether lifestyle factors need adjustment. Some people respond better to alternative GLP-1 medications. Your prescriber will work with you to find the right approach rather than simply stopping treatment.
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.