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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How Long Do You Stay on Mounjaro vs Wegovy?
If you're considering prescription weight loss treatment in the UK, understanding how long you'll take Mounjaro or Wegovy is important. Both medications follow a dose titration schedule and are typically used as long-term treatments, but they differ in timing and mechanism. Mounjaro uses a dual GIP and GLP-1 approach with weekly increases, while Wegovy is a GLP-1 agonist only. Your GP or prescriber will assess which suits your individual needs following a clinical assessment.
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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 vs Wegovy: Timeline and Dose Escalation
Mounjaro (tirzepatide) follows a 4-week dose escalation schedule. You start at 2.5 mg weekly for weeks 1–4, then increase to 5 mg, 7.5 mg, 10 mg, 12.5 mg, and finally 15 mg (the maximum dose). The minimum time between dose increases is 4 weeks, meaning it takes approximately 24 weeks (6 months) to reach the maximum maintenance dose. Each dose is a once-weekly injection delivered via a KwikPen device.
Wegovy (semaglutide) has a faster initial escalation. You begin at 0.25 mg for weeks 1–4, then increase weekly to 0.5 mg, 1 mg, and 1.7 mg. The maximum dose of 2.4 mg is typically reached by week 17 (around 4 months). Clinical trials showed Wegovy helps participants lose an average of approximately 15% body weight—individual results vary significantly.
- Mounjaro reaches max dose in approximately 6 months
- Wegovy reaches max dose in approximately 4 months
- Both require minimum 4-week intervals between increases
- Both are once-weekly injections
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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.
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How Long Will You Take These Medications?
Both Mounjaro and Wegovy are intended as long-term treatments, not short-term interventions. Clinical trial data from SURMOUNT-1 (Mounjaro) showed participants maintained weight loss improvements over 72 weeks. For Wegovy, the STEP trials demonstrated sustained weight loss benefits over approximately 68 weeks. Most people continue these medications as long as they remain effective and well-tolerated, often indefinitely or until a prescriber advises otherwise.
Your prescriber will review your progress regularly and assess whether to continue, adjust the dose, or explore alternatives. If you stop either medication, weight may gradually return over time. Use our free GLP-1 weight loss calculator to explore potential outcomes with either medication, and discuss the most appropriate option with your GP or prescriber following a clinical assessment.
- 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.
Which medication works faster—Mounjaro or Wegovy?
Wegovy reaches its maximum dose more quickly (around 4 months vs 6 months for Mounjaro), but "faster" does not mean "more effective." Mounjaro's dual mechanism may deliver greater average weight loss in clinical trials (~21% vs ~15%), though individual results vary. Prescriber assessment determines which suits you best.
How long before you see results on Mounjaro or Wegovy?
Weight loss typically begins within 2–4 weeks at therapeutic doses. Most noticeable changes appear after 8–12 weeks. Clinical trials measured major results at 16+ weeks. Results depend on dose, diet, activity level, and individual metabolism. Track progress using our free progress tracker.
Can you stay on Mounjaro or Wegovy indefinitely?
Yes, both are designed for long-term use. Many people continue these medications long-term alongside lifestyle changes. Your GP will review progress regularly and advise on duration. These are not short-term treatments. Stopping either may result in gradual weight regain.
What if Mounjaro or Wegovy stops working?
If weight loss plateaus, your prescriber may adjust your dose, review your diet and activity, assess for medical causes, or explore alternatives. Some individuals respond better to one medication than the other. A clinical assessment will determine the best next step for your situation.
Do you need a prescription to get Mounjaro or Wegovy in the UK?
Yes, both are prescription-only medicines. In the UK, you can access these through NHS specialist weight management services (referral from GP required) or private prescribing following an online clinical assessment with a UK-licensed prescriber. Use our BMI calculator to check your eligibility based on NHS criteria.
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.