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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Why Weight Loss Stalls on Mounjaro
Weight loss plateaus are common when taking Mounjaro (tirzepatide), even when you're following your reduced-calorie diet and exercise routine properly. A stall doesn't mean the medication isn't working — it often means your body has adapted to your current dose or calorie intake. Understanding why this happens and what options are available can help you decide whether a dose increase, lifestyle adjustment, or a different medication like Wegovy might be right for you. This guide explains what causes stalling on Mounjaro and how to move forward.
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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 Stalling vs Wegovy — Mechanism and Trial Data
Mounjaro (tirzepatide) works through a dual GIP and GLP-1 receptor agonist mechanism, whilst Wegovy (semaglutide) activates GLP-1 only. In the SURMOUNT-1 clinical trial, Mounjaro at 15 mg achieved an average weight loss of approximately 20.9% of body weight over 72 weeks. The STEP-1 trial showed Wegovy at 2.4 mg achieved around 14.9% average weight loss over 68 weeks. However, individual responses vary significantly — some people respond better to Mounjaro's dual mechanism, whilst others find Wegovy more effective or tolerable.
- Mounjaro dose range: 2.5 mg to 15 mg once weekly, with minimum 4 weeks at each dose before escalating
- Wegovy dose range: 0.25 mg to 2.4 mg once weekly, with a slower titration schedule
- Key difference: Mounjaro's GIP pathway may provide additional appetite suppression for some users, but it also means more people experience gastrointestinal side effects early in treatment
If you're stalling on Mounjaro, your prescriber may increase your dose, but it's also worth considering whether the medication's mechanism is the right fit for your body.
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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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When to Escalate, Switch, or Adjust Lifestyle
A weight loss plateau after 4–8 weeks on your current Mounjaro dose is often a signal that escalation is due. If you haven't reached the maximum dose of 15 mg, your prescriber may recommend increasing to the next dose level — provided you've been on your current dose for at least 4 weeks and side effects are manageable. However, not all stalls require medication changes. Calorie creep (eating more without realising), reduced physical activity, or metabolic adaptation can all cause plateaus. Some people also find that switching from Mounjaro to Wegovy, or vice versa, reignites weight loss when their body has adapted to one mechanism.
Use our GLP-1 weight loss calculator to project potential outcomes at different doses, and our free progress tracker to identify whether your plateau is genuine (no weight change for 3+ weeks) or normal fluctuation. Always discuss any changes with your prescriber — they can assess your individual response and recommend the next step.
- 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.
Why does weight loss stall on Mounjaro even though I'm following my diet?
Weight loss plateaus are a normal part of the weight loss journey. Your body adapts to both the medication and calorie deficit. Metabolic adaptation, hormonal changes, and reduced physical activity can all contribute. Stalling doesn't mean Mounjaro isn't working — it may mean your dose needs increasing or your lifestyle adjustments need tweaking. Your prescriber can help identify the cause.
Is Wegovy better than Mounjaro if I'm stalling?
Not necessarily. Both medications use different mechanisms — Mounjaro is a dual GIP+GLP-1 agonist, whilst Wegovy is GLP-1 only. Some people respond better to one than the other, but there's no objective "better" medication. SURMOUNT trial data shows Mounjaro achieved slightly higher average weight loss than Wegovy's STEP trials, but individual results vary. Your prescriber can advise whether switching is worth trying.
How long should I wait before asking about a dose increase?
You should be on your current Mounjaro dose for at least 4 weeks before your prescriber considers escalation. If you've been stable on a dose for 4–8 weeks with no further weight loss and no contraindications, a dose increase is a reasonable next step. However, your prescriber may first review your diet, activity level, and whether side effects are limiting your compliance.
Can I switch from Mounjaro to Wegovy mid-treatment?
Yes, it's possible to switch between medications, though this should only be done under prescriber guidance. There's no official established conversion between Mounjaro and Wegovy doses — your prescriber will restart you on an appropriate dose for Wegovy. Some people find switching reignites weight loss after adapting to Mounjaro's mechanism, but others don't see improvement.
What if I'm on maximum Mounjaro dose and still stalling?
If you've reached 15 mg Mounjaro and weight loss has plateaued, your prescriber may suggest switching to Wegovy, reviewing your calorie intake, or increasing physical activity. Alternatively, a plateau at maximum dose may represent your body's natural settling point. Your GP can discuss whether continued medication is still appropriate or whether lifestyle maintenance is the next phase. ```
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