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
How Quickly Does Mounjaro Work in the UK?
Mounjaro (tirzepatide) starts working within days of your first injection, but noticeable weight loss typically appears after 2-4 weeks. Most people see more significant results over 8-12 weeks as the dose escalates. The Mounjaro KwikPen requires dose titration — you begin at 2.5 mg weekly and increase gradually over 16+ weeks to reach the maximum 15 mg dose. How quickly you see results depends on your starting weight, lifestyle changes, and individual metabolism. Understanding both the timeline and how to access Mounjaro in the UK — whether through NHS specialist services or private prescription — helps you set realistic expectations and plan your weight management journey effectively.
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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 Timeline: When You'll See Results
Mounjaro begins working immediately after injection, as tirzepatide activates GLP-1 and GIP receptors within hours. However, the timeline to noticeable weight loss follows the dose escalation schedule.
- Weeks 1-4 (2.5 mg): Appetite suppression may begin; most people report reduced hunger within 3-7 days
- Weeks 5-8 (5 mg): Modest weight loss typically appears, averaging 2-4 kg for most people
- Weeks 9-16 (7.5-10 mg): Weight loss accelerates; more noticeable changes in how clothes fit
- Weeks 17+ (12.5-15 mg): Steady weight loss continues; clinical data shows average loss of 15-21% body weight at the highest doses
The dose titration process means results build gradually rather than rapidly. Your prescriber will adjust your dose every 4 weeks based on how you respond and tolerate side effects. Individual results vary significantly depending on diet adherence, physical activity, and individual metabolism.
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.
Accessing Mounjaro: NHS vs Private Prescription Costs
NHS access: Mounjaro is approved by NICE for NHS specialist weight management services (tier 3/4), but availability varies by region and waiting lists can extend months or years in many areas. Your GP refers you to a specialist weight management service, where a consultant assesses your eligibility based on BMI, comorbidities, and NHS criteria.
Private prescription: Available through UK-licensed prescribers via online consultation, costing approximately £129-£320 per month depending on your dose and provider. No NHS referral needed — you complete an online health assessment, and if approved, receive a prescription dispensed by a GPhC-registered pharmacy. Private access offers faster availability but requires payment.
Both routes require a clinical assessment to confirm you meet eligibility criteria (BMI 30+ or 27+ with weight-related health conditions). Try our free BMI calculator above to check where you stand, and our GLP-1 weight loss calculator to estimate potential results with Mounjaro 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.
How quickly will I lose weight on Mounjaro?
Weight loss typically becomes noticeable after 2-4 weeks, with more significant results appearing over 8-12 weeks as your dose increases. Clinical trials showed average weight loss of 15-21% body weight at the maximum 15 mg dose. However, individual results vary based on diet, exercise, starting weight, and personal metabolism. Results are not assured.
What does the Mounjaro KwikPen dose titration schedule look like?
You start at 2.5 mg weekly for 4 weeks, then increase by 2.5 mg every 4 weeks: 5 mg, 7.5 mg, 10 mg, 12.5 mg, and finally 15 mg (the maximum). Your prescriber may adjust the pace based on side effects and tolerance. The full escalation typically takes 16-20 weeks to reach your target maintenance dose.
Can I get Mounjaro on the NHS in the UK?
Yes — Mounjaro is approved by NICE for NHS use through specialist tier 3/4 weight management services. However, access varies significantly by region, and waiting lists can be very long (months to years). You need a GP referral to a local specialist service. Private prescription options offer faster access without NHS referral.
How much does Mounjaro cost on private prescription in the UK?
Private Mounjaro typically costs £129-£320 per month depending on your dose and provider. Costs may increase as you escalate to higher doses. This is paid privately and is not covered by the NHS (except through specialist services). Always check with your provider for exact pricing before starting treatment.
How long does Mounjaro stay in your system after you stop?
Tirzepatide has a half-life of approximately 5 days, meaning about half the drug leaves your body every 5 days. After stopping, effects diminish over 2-4 weeks, though appetite suppression may linger slightly longer. Weight loss achieved is maintained only if lifestyle changes (diet and exercise) continue; without ongoing healthy habits, weight regain can occur.
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.