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
Why Has Your Mounjaro Weight Loss Slowed Down?
If your weight loss has slowed or plateaued after starting Mounjaro (tirzepatide), you're not alone — this is a common experience during treatment. Weight loss on Mounjaro typically follows a pattern of initial rapid loss followed by gradual slowing, which is actually normal and expected. Understanding why this happens, and what steps you can take next, helps you stay on track with your weight management goals. Our GLP-1 weight loss calculator can help you explore realistic expectations at different doses.
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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.
Why Weight Loss Naturally Slows on Mounjaro
Weight loss on Mounjaro generally follows a predictable pattern. Initial weight loss (weeks 1–12) is often faster as your body adapts to reduced calorie intake and the medication's appetite-suppressing effects. As weeks progress, weight loss naturally slows — this is physiological adaptation, not treatment failure.
Several factors cause this slowdown:
- Metabolic adaptation: As you lose weight, your metabolic rate slightly decreases, requiring additional calorie deficit to continue losing weight
- Medication tolerance: Some people experience reduced appetite suppression over time as their body adapts to tirzepatide
- Dose plateau: If you've reached your target dose (up to 15 mg weekly), further increases aren't possible
- Lifestyle drift: Without continued focus on diet and physical activity, weight loss naturally slows
Clinical trial data (SURMOUNT-1) shows most significant weight loss occurs in the first 16–20 weeks, then continues more gradually. This is expected and normal.
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
What Options Are Available If Weight Loss Slows
If your Mounjaro weight loss has plateaued, discuss these options with your prescriber:
- Dose increase: If you're not yet on the maximum 15 mg dose, your prescriber may increase your dose — each escalation typically requires 4 weeks at the current dose before increasing
- Dietary review: Work with a dietitian to identify any calorie creep or hidden sources of calories — weight loss plateaus often indicate the calorie deficit has narrowed
- Physical activity: Increasing exercise, particularly resistance training, can help restart weight loss and preserve muscle mass
- Consistency check: Confirm you're injecting on schedule and storing your KwikPen correctly
Use our free progress tracker to monitor weekly patterns — sometimes weight loss is happening but masked by natural fluctuations in fluid retention.
- 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.
Is a weight loss plateau on Mounjaro permanent?
No. Weight loss plateaus are temporary and normal. Most commonly, they're addressed by dose increases (if you haven't reached 15 mg), dietary adjustments, or increased physical activity. Some people experience renewed weight loss after making these changes. Always discuss with your prescriber before making changes.
How long does it take for Mounjaro weight loss to resume after a dose increase?
After a dose increase, you typically inject the new dose once weekly for 4 weeks before the full effect is seen. Some people notice appetite suppression changes within days; others take 2–3 weeks. Individual response varies. Your prescriber will advise you on realistic timelines.
Can I skip a dose of Mounjaro to "reset" my weight loss?
No. Skipping doses is not recommended and may reduce treatment effectiveness. Tirzepatide works best with consistent weekly dosing. If you're concerned about weight loss slowing, contact your prescriber to discuss dose adjustment or other options — never change your injection schedule without guidance.
What's the difference between Mounjaro slowing weight loss and Mounjaro not working?
Mounjaro "working" means it's reducing appetite and supporting a calorie deficit. Slowed weight loss is normal — it doesn't mean the medication has stopped working. You're still in a calorie deficit; it's just smaller than during the gradual weight management phase. Your prescriber can clarify whether the medication is still effective for you.
Should I switch from Mounjaro to Wegovy if my weight loss slows?
Switching medications (like moving to Wegovy, a GLP-1-only injection) is a decision for your prescriber. Mounjaro's dual GIP/GLP-1 mechanism may be more effective for some people than single GLP-1 medications. However, if you've hit a genuine plateau after maxing out dose, a switch might be explored. Always discuss options with your prescriber.
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.