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 2.5 Mg Mounjaro Might Not Be Showing Results Yet
If you're on 2.5 mg Mounjaro and aren't seeing weight loss results, you're likely still in the starting phase — this dose is designed for tolerance and adjustment, not maximum effect. Mounjaro works gradually, and 2.5 mg is typically continued for only 4 weeks before escalating. Individual response varies considerably, and several factors influence whether you notice changes at this early stage. Understanding the timeline and when to expect adjustments with your prescriber can help clarify what's normal and what may need reviewing.
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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.
Understanding the 2.5 Mg Starting Dose Timeline
2.5 mg is an adjustment dose, not a maintenance dose. In the SURMOUNT clinical trials of tirzepatide (Mounjaro), the 2.5 mg starting dose is held for exactly 4 weeks before increasing. This initial phase allows your body to tolerate the medication and adjusts your appetite signals gradually. Weight loss acceleration typically occurs at higher doses — the 5 mg, 10 mg, 15 mg escalations where the full therapeutic effect becomes apparent.
- Weeks 1–4: 2.5 mg dose (tolerance phase)
- Week 5 onwards: Typically increased to 5 mg (where measurable results often begin)
- Average weight loss at 2.5 mg alone is modest — clinical trials show significant results at 10 mg and 15 mg doses
- Your GP or prescriber should increase your dose after 4 weeks if you've tolerated 2.5 mg without serious side effects
If you've been on 2.5 mg for longer than 4 weeks without escalation, discuss dose progression with your prescriber — you may be ready to move up.
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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.
Factors That Influence Early Results on Mounjaro
Weight loss on any GLP-1 or GIP/GLP-1 medication depends on several factors beyond dose alone. Diet and activity matter significantly — Mounjaro works best alongside a reduced-calorie diet and regular physical activity. Individual metabolism, starting weight, age, and genetics all affect how quickly you see changes on the scale. Some people notice appetite suppression and fullness signals immediately; others experience a more gradual shift. Additionally, early weeks may show non-scale changes — improved energy, reduced cravings, or better blood sugar control — before visible weight loss appears.
Use our free GLP-1 weight loss calculator to estimate potential results at higher doses, and track progress with our progress tracker to capture all improvements, not just weight.
- 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.
Should I increase my Mounjaro dose if 2.5 mg isn't working?
Not by yourself — only your prescriber can adjust your dose. Standard protocol is to increase after 4 weeks on 2.5 mg if you've tolerated it well. Contact your GP or online prescriber if you've been on 2.5 mg for longer than 4 weeks without dose escalation, as progression to 5 mg is typically next.
How long does it take to see weight loss on Mounjaro?
Results vary significantly between individuals. Some people notice appetite changes within days; weight loss may take 2–4 weeks at therapeutic doses (5 mg and above). Clinical trials show more pronounced results after 8–12 weeks of consistent use at adequate doses alongside lifestyle changes.
Is 2.5 mg Mounjaro ever a maintenance dose?
No — 2.5 mg is exclusively a starting/titration dose. It's designed for a 4-week adjustment period only. Your prescriber will increase to 5 mg after week 4, and may continue escalating based on tolerance and response.
Can I add diet and exercise to speed up results on 2.5 mg?
Yes — diet and exercise are essential at every dose. A reduced-calorie diet (approximately 500 kcal deficit daily) combined with regular physical activity significantly improves results. Mounjaro alone, without lifestyle changes, is much less effective. Use our BMI calculator to establish your baseline and track progress.
What if I tolerate 2.5 mg well but see no appetite change?
Lack of noticeable appetite suppression at 2.5 mg is common — this dose is low and designed primarily for tolerance. Most people experience clearer appetite-related effects at 5 mg and higher. Report this to your prescriber so you can progress to the next dose on schedule. Individual response timing varies. ```
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.