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 Mounjaro 2.5mg Might Not Be Working Yet
If you've started Mounjaro at the 2.5mg dose and haven't noticed weight loss yet, this is completely normal — 2.5mg is a starting dose designed to help your body adjust, not deliver maximum results. Mounjaro (tirzepatide) works gradually, and most people require dose escalation over several weeks before significant weight loss occurs. Understanding how the medication is meant to work, and what realistic expectations are at the starting dose, can help you stay on track with your treatment plan.
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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.
The 2.5mg Dose Is a Starting Point, Not the Target
Mounjaro uses a dose titration schedule, meaning you start low and gradually increase. The 2.5mg dose (weeks 1–4) serves two main purposes: to allow your body to adjust to the medication and to assess tolerability before moving to higher doses. Clinical evidence shows that meaningful weight loss typically occurs at higher doses — the SURMOUNT-1 trial demonstrated average weight loss of approximately 15% at 5mg, rising to 20.9% at the maximum 15mg dose.
Many people experience minimal weight change in the first 4 weeks on 2.5mg. This is expected. Your prescriber will review your progress after this initial period and, if appropriate, increase your dose to 5mg for weeks 5–8. Weight loss typically becomes more noticeable once you reach 5mg or higher.
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.
Realistic Timelines and What Affects Response
Weight loss on Mounjaro is individual — some people see changes sooner than others, but most require at least 8–12 weeks to notice meaningful results. Factors affecting your response include diet adherence (Mounjaro works best alongside a reduced-calorie diet), physical activity level, metabolism, previous dieting history, and other medications you're taking.
If you're on 2.5mg, your first priority is completing the 4-week period and then discussing dose escalation with your prescriber. Use our free GLP-1 weight loss calculator to track projected outcomes at different doses, and our progress tracker to log weekly measurements — sometimes subtle changes show in measurements before visible weight loss occurs.
- 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 2.5mg Mounjaro supposed to work for weight loss?
2.5mg is a starting and adjustment dose, not a therapeutic dose. It's designed to help your body tolerate the medication before escalation. Meaningful weight loss typically happens at 5mg and above. Most people need to progress through dose increases to see significant results.
How long should I stay on 2.5mg Mounjaro?
You should remain on 2.5mg for 4 weeks. Your prescriber will then review your progress and tolerability. If appropriate, your dose will increase to 5mg for the next 4 weeks, continuing upward every 4 weeks until you reach an effective maintenance dose (often 10mg or higher).
What if I'm not losing weight after 8 weeks on Mounjaro?
If you've progressed to 5mg or higher and aren't seeing results after 8–12 weeks, speak to your prescriber. They may increase your dose further, review your diet and activity level, or investigate whether other factors (medications, medical conditions) are affecting your response.
Should I skip the 2.5mg dose and start higher?
No — never skip dose titration without medical guidance. Starting at 2.5mg reduces side effects and helps your body adjust safely. Jumping to higher doses increases nausea, vomiting, and other gastrointestinal side effects without improving weight loss outcomes.
How does Mounjaro compare to Wegovy at the starting dose?
Wegovy starts at 0.25mg (much lower), while Mounjaro starts at 2.5mg. However, the principle is identical — both medications use gradual dose escalation. Mounjaro's dual GIP/GLP-1 mechanism may produce results at higher doses; Wegovy's single GLP-1 mechanism has similar average outcomes across trials, but individual results vary significantly.
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.