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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Not Losing Weight on Mounjaro 5mg — What to Know
If you're on Mounjaro 5mg and not seeing weight loss yet, you're not alone — and it doesn't necessarily mean the medication isn't working for you. Mounjaro is typically started at 2.5mg and gradually increased, so 5mg is still an early dose for many people. This guide explains why initial weight loss may be slow, how Mounjaro compares to Wegovy (another weekly weight loss injection), and what to discuss with your prescriber. Use our free GLP-1 weight loss calculator to explore potential outcomes 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 May Be Slow at 5mg — Trial Data and Dose Escalation
Mounjaro works gradually. In the SURMOUNT-1 clinical trial, the average weight loss at 5mg was approximately 15% of body weight — but this was measured after participants had titrated through all doses over 72 weeks. At 5mg specifically (usually weeks 5–8), many people are still in the early adjustment phase.
Your body is adapting. It takes time for your system to respond to a weekly weight loss injection. Side effects like nausea often reduce after a few weeks, and appetite suppression may increase as you continue dosing.
Dose escalation matters. Mounjaro's standard dose titration is: 2.5mg (weeks 1–4), 5mg (weeks 5–8), 7.5mg (weeks 9–12), up to 15mg maximum. Most meaningful weight loss occurs at higher maintenance doses. If you've only recently reached 5mg, your prescriber may recommend continuing to the next dose step after the minimum 4-week interval.
- Track your progress with our free progress tracker to monitor changes beyond the scale
- Weight loss is rarely linear — expect plateaus and fluctuations
- Individual results vary significantly based on diet, activity, and metabolism
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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.
Mounjaro 5mg vs Wegovy — Mechanism and Trial Outcomes
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two different hormone pathways. In trials, average weight loss was around 15% on the 5mg equivalent dose. Wegovy (semaglutide) is a GLP-1 agonist only (single mechanism), with average weight loss around 14.9% in the STEP-1 trial.
The difference is modest at lower doses, but Mounjaro's dual mechanism may offer advantages as you escalate to higher maintenance doses (10mg, 15mg). However, both medications require a prescription and clinical assessment — your prescriber will decide which is more suitable based on your individual health and medical history. Use our BMI calculator to establish your baseline, and discuss any concerns about weight loss speed with your healthcare provider. Neither medication assures rapid loss.
- 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 5mg Mounjaro the maximum dose?
No. 5mg is typically weeks 5–8 of the standard titration schedule. The dose escalates every 4 weeks up to a maximum of 15mg weekly. Most significant weight loss occurs at higher maintenance doses (10–15mg). Your prescriber will guide you through escalation if appropriate.
How long before I should expect weight loss on Mounjaro 5mg?
Weight loss timelines vary. Some people notice appetite suppression within days, others take weeks. At 5mg specifically, you're still early in treatment. Continue for at least 4 weeks at this dose before escalating, and track progress over several weeks rather than daily. Your prescriber can advise on your individual trajectory.
Is Wegovy better than Mounjaro if I'm not losing weight?
Not necessarily. Both are prescription-only weekly weight loss injections with similar average results at comparable doses. Wegovy uses a single GLP-1 mechanism, Mounjaro a dual GIP+GLP-1 mechanism. Individual suitability depends on your health profile. Discuss switching options with your prescriber rather than self-deciding.
Should I increase my Mounjaro dose early if I'm not losing weight?
No. Dose increases are typically spaced 4 weeks apart to allow your body to adapt and minimise side effects. Increasing too quickly may increase nausea and other side effects without improving outcomes. Follow your prescriber's dose escalation plan.
What if I'm on Mounjaro 5mg and genuinely not responding?
Speak to your prescriber. Non-response can relate to diet, activity level, underlying health conditions, or medication interaction. Your prescriber may recommend continuing to the next dose, reviewing lifestyle factors, or discussing alternative options. Weight loss medications work best alongside reduced-calorie diet and physical activity.
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.