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 Is Mounjaro At Its Peak in the UK?
Mounjaro reaches its peak effect after around 16–20 weeks of treatment, once you've completed the dose titration schedule and stabilised on your maintenance dose. Understanding when Mounjaro works at its strongest, how much it costs in the UK, and your options for accessing tirzepatide will help you plan your weight management journey effectively. Whether you're considering NHS access through specialist services or exploring private prescription options, knowing the timeline and costs involved is important for making an informed decision.
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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.
Peak Effectiveness Timeline and Cost in the UK
Mounjaro reaches peak effectiveness after approximately 16–20 weeks once you've completed the full dose titration schedule and stabilised on your maintenance dose (typically 10 mg or 15 mg). This timeline accounts for the gradual escalation: 2.5 mg weeks 1–4, 5 mg weeks 5–8, 7.5 mg weeks 9–12, 10 mg weeks 13–16, and 15 mg from week 17 onwards.
In terms of cost, private Mounjaro prescriptions in the UK typically range from £149 to £320 per month depending on your dose and the private provider. This cost covers the online consultation, clinical assessment, and prescription dispensing. A KwikPen (containing 4 weekly doses) usually costs between £150 and £300 privately. NHS access is available through specialist tier 3 weight management services, but availability varies significantly by region and waiting lists can be substantial. Your GP can refer you to your local NHS specialist service, though access is not assured everywhere.
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.
NHS vs Private Access: Which Route Suits You?
NHS route: Free at point of use once prescribed, but requires referral to a specialist weight management service and may involve lengthy waiting periods. NICE has approved tirzepatide for NHS use, but regional variation in commissioning means availability depends on your ICB (Integrated Care Board) area.
Private route: Faster access without NHS referral. An online consultation with a UK-licensed prescriber (typically £30–£50) determines if Mounjaro is suitable for you based on your BMI, health history, and eligibility criteria. If approved, your prescription is dispensed by a GPhC-registered pharmacy. Use our GLP-1 weight loss calculator to estimate potential results at different doses, and our BMI calculator to confirm your eligibility before starting the online assessment process.
- 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 before Mounjaro works at full strength?
Mounjaro reaches peak effectiveness after 16–20 weeks once you've completed the full dose escalation. Most people stabilise on a maintenance dose (10 mg or 15 mg) by week 16–17. Individual response varies, and your prescriber may adjust timing based on your weight loss progress and side effects.
What's the difference between Mounjaro and Wegovy in terms of timing?
Both reach peak effect at similar timeframes (around 16–20 weeks), but tirzepatide (Mounjaro) is a dual GIP/GLP-1 agonist while semaglutide (Wegovy) is GLP-1 only. Mounjaro's dual mechanism may produce earlier satiety signals, but individual timing varies. Clinical trials showed comparable weight loss averages after stabilisation.
Can I access Mounjaro through the NHS in the UK?
Yes, NICE has approved tirzepatide (Mounjaro) for NHS prescription through specialist tier 3 weight management services. However, availability varies by region and waiting lists can be long. Your GP can refer you, but commissioning decisions depend on your local ICB. Private access is typically faster.
What happens if Mounjaro doesn't work for me at peak dose?
If you're not seeing the expected weight loss results at your peak maintenance dose after 20+ weeks, your prescriber may review your dose, check for medication interactions, or discuss switching to an alternative GLP-1 medication. Lifestyle factors like diet and physical activity are equally important — Mounjaro works best alongside a reduced-calorie diet.
Is the cost of private Mounjaro the same across all UK pharmacies?
No, private Mounjaro costs vary between providers. Expect £149–£320 per month depending on dose and supplier. Some providers include repeat consultations, others charge separately. Always check what's included (consultation, prescription, follow-up support) before choosing a provider. Never buy from unregistered sources.
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.