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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When Does Mounjaro Peak and How to Access It in the UK
Mounjaro (tirzepatide) typically reaches its peak effectiveness after 4–5 weeks at each dose level, with maximum effects generally seen around 12–16 weeks of treatment. Understanding when Mounjaro peaks helps you know what to expect during your weight management journey. This guide explains how the medication works, when you'll likely see results, and how to access Mounjaro in the UK through NHS specialist services or private prescription routes. Whether you're considering this dual GIP and GLP-1 receptor agonist or already using a Mounjaro KwikPen, knowing the timeline helps set realistic expectations alongside a reduced-calorie diet and increased physical activity.
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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 Mounjaro Works and When It Reaches Peak Effect
Mounjaro reaches peak effectiveness gradually as your body adjusts to each dose. The medication is a prescription-only dual GIP and GLP-1 receptor agonist that works by activating two natural hormone pathways to regulate appetite and support weight management. You start on 2.5 mg weekly, then typically increase by 2.5 mg every 4 weeks until reaching your target dose (usually 10–15 mg). At each dose level, peak effect is achieved around week 4–5, meaning you'll experience maximum appetite suppression and fullness signals at that point before increasing.
- Week 1–4 at each dose: body adjusts, side effects may vary, effects build gradually
- Week 5 onwards: peak effectiveness at that dose level is reached
- Dose titration: minimum 4 weeks between increases to assess tolerance
- Total timeline: full effects across all doses typically seen by week 12–16 of treatment
- Individual variation: some people peak sooner, others take longer to reach full effect
Clinical trials showed that results continue to improve as doses increase, with average weight loss of approximately 15–21% body weight on the maximum 15 mg dose. However, individual results vary significantly based on lifestyle factors, adherence, and personal physiology. Our free GLP-1 weight loss calculator can help you estimate potential outcomes at different dose levels.
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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.
UK Cost, Access Routes, and How to Get Mounjaro
In the UK, accessing Mounjaro depends on whether you go through the NHS route or private prescription. NHS access is through specialist tier 3 weight management services via GP referral—availability varies significantly by region, and waiting lists can be several months to over a year in many areas. Private route cost typically ranges from £129–£320 per month depending on your dose and the prescribing service, with monthly costs increasing at higher doses.
- NHS: free once referred to specialist services, but limited availability and long waits
- Private prescription: £129–£180 for doses 2.5–7.5 mg; £180–£320 for doses 10–15 mg per month
- Online consultation: assessment with UK-licensed prescriber, prescription issued if suitable, dispensed by GPhC-registered pharmacy
- No requirement for NHS referral with private route—faster access but you pay directly
Both routes require a clinical assessment to confirm eligibility. You'll need a BMI of 30+ or 27+ with weight-related health conditions. Our BMI calculator above can help you check where you stand against 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.
When will I see weight loss results with Mounjaro?
Most people notice reduced appetite within the first 2–4 weeks, but measurable weight loss typically becomes apparent after 4–8 weeks of consistent use. Peak appetite suppression is reached 4–5 weeks after each dose increase. Clinical trials showed average weight loss of 15–21% over 72 weeks, but individual results vary significantly based on diet, exercise, and adherence.
What's the difference between when Mounjaro peaks and when I'll lose weight?
Peak effectiveness (maximum appetite suppression) is reached around week 4–5 at each dose. Weight loss follows as a result of eating less due to reduced appetite. You typically won't see significant weight loss immediately—it accumulates over weeks and months as the calorie deficit builds. This is why the dose titration schedule is 4+ weeks: to allow peak effect and assess whether you need to increase.
Is Mounjaro available on the NHS, and how long is the wait?
Yes, Mounjaro (tirzepatide) is approved by NICE for NHS specialist weight management services, but access is limited. You must be referred by your GP to a tier 3 service in your area. Waiting times vary dramatically by region—some areas have waits of 6–12 months or longer. Private prescription offers faster access without NHS referral, at a cost of £129–£320 monthly depending on dose.
How do I get a Mounjaro prescription privately in the UK?
Book an online consultation with a UK-licensed prescriber through a private prescribing service. The prescriber will assess your medical history, BMI, and health conditions. If approved, they'll issue a prescription to a GPhC-registered pharmacy for dispensing. The entire process typically takes 1–3 days. You'll need a BMI of 30+ or 27+ with weight-related conditions to be eligible. Costs vary by dose and provider.
How much does Mounjaro cost monthly in the UK privately?
Private costs depend on your dose. Lower doses (2.5–5 mg) cost approximately £129–£160 monthly. Mid-range doses (7.5–10 mg) cost £160–£220 monthly. Higher doses (12.5–15 mg) cost £220–£320 monthly. Prices vary between prescribing services, so it's worth comparing. Most people start on 2.5 mg and increase gradually, so initial costs are lower than maximum-dose costs.
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.