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
Does Mounjaro Wear Off? Mounjaro vs Wegovy Explained
Many UK adults wonder what happens when Mounjaro wears off between injections, and whether Wegovy might be a better alternative. Both are prescription-only weight management injections licensed in the UK, but they work differently and have different effects over time. This guide explains how each medication maintains its effect, compares their mechanisms, and helps you understand which might be more suitable following clinical assessment by a prescriber.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 and Wegovy Maintain Their Effect Over Time
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways simultaneously. This dual mechanism may contribute to a more sustained appetite-suppressing effect throughout the week, with many users reporting consistent appetite reduction even as the injection dose begins to wear off towards day 7. The SURMOUNT clinical trials showed average weight loss of 15–21% body weight over 72 weeks at maximum dose (15 mg).
Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single hormone pathway. Its effect may be slightly more variable week-to-week for some users, though clinical data from the STEP trials demonstrated average weight loss of approximately 15% body weight at the maximum 2.4 mg dose over 68 weeks. Wegovy's once-weekly injection provides consistent dosing like Mounjaro, but the single mechanism may feel different in terms of appetite suppression pattern throughout the week.
Neither medication "wears off" completely between doses in the traditional sense—residual effects persist. However, some users report noticing a subtle difference in appetite control by day 6 or 7 before their next injection. This is individual variation and not a sign of treatment failure.
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.
Which Medication Might Be Right for You? The Prescriber Decision
Both Mounjaro and Wegovy require a UK prescription and clinical assessment before being dispensed. A prescriber will evaluate your individual health profile, BMI, existing health conditions, and any previous medication responses to recommend the most suitable option. Your MyWeightCheck BMI calculator can help you understand your starting BMI before your assessment, though the prescriber's clinical judgment is what determines suitability.
Key differences: Mounjaro's dual mechanism may be more effective for some users; Wegovy has longer established safety data in the UK market. Mounjaro starts at 2.5 mg weekly and escalates to 15 mg maximum. Wegovy starts at 0.25 mg and escalates to 2.4 mg maximum. Both are used alongside reduced-calorie diet and increased physical activity. Individual results vary significantly. If one medication isn't working as hoped, switching is possible with prescriber guidance, but this requires reassessment.
Both Mounjaro and Wegovy require a UK prescription and clinical assessment before being dispensed. A prescriber will evaluate your individual health profile, BMI, existing health conditions, and any previous medication responses to recommend the most suitable option. Your MyWeightCheck BMI calculator can help you understand your starting BMI before your assessment, though the prescriber's clinical judgment is what determines suitability.
Key differences: Mounjaro's dual mechanism may be more effective for some users; Wegovy has longer established safety data in the UK market. Mounjaro starts at 2.5 mg weekly and escalates to 15 mg maximum. Wegovy starts at 0.25 mg and escalates to 2.4 mg maximum. Both are used alongside reduced-calorie diet and increased physical activity. Individual results vary significantly. If one medication isn't working as hoped, switching is possible with prescriber guidance, but this requires reassessment.
- 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.
Does Mounjaro actually wear off between injections?
Mounjaro doesn't completely wear off—residual effects persist throughout the week. However, some users notice appetite suppression is strongest on days 1–3 after injection, with a subtle reduction by day 6–7. This is normal and individual. If you feel significantly hungrier before your next dose, mention this to your prescriber; a dose increase may help, or medication switching may be appropriate.
Is Wegovy more or less effective than Mounjaro if it "wears off" more noticeably?
Clinical trial data doesn't show Wegovy "wearing off" more than Mounjaro; rather, they use different mechanisms. Mounjaro's dual GIP+GLP-1 action may feel more consistent for some users, whilst Wegovy's single GLP-1 mechanism is equally effective but may feel different individually. Effectiveness depends on your personal response, not the mechanism alone.
What should I do if I feel Mounjaro isn't working as well by the end of the week?
Contact your prescriber. Options include: waiting for your next dose, increasing to the next Mounjaro dose (if not at maximum), or discussing a potential switch to Wegovy or another medication. Never adjust timing or dosing yourself. A prescriber can assess whether your BMI is progressing, whether side effects are limiting, or whether a different approach is needed.
Can I switch from Mounjaro to Wegovy if Mounjaro isn't working for me?
Yes, switching between medications is possible with prescriber guidance. Approximate dose equivalence exists (Mounjaro 10 mg ≈ Wegovy 1.7 mg), but any switch requires clinical reassessment. Your prescriber will ensure a safe transition and monitor your progress using tools like weight tracking and BMI monitoring to confirm the new medication is working.
How long does it take to see results with either medication?
Most users notice appetite reduction within 1–2 weeks of starting. Measurable weight loss (1–2 kg) typically appears within 4–8 weeks, though this varies. Maximum results usually appear around 16–20 weeks as doses escalate. Use our free progress tracker to log weekly weight changes and see trends clearly—this helps you and your prescriber assess whether the medication is working effectively for you.
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.