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 Your 2.5 Mg Mounjaro Dose May Not Be Working Yet
If you've started Mounjaro at the 2.5 mg starting dose and aren't seeing weight loss results, you're not alone—and this doesn't necessarily mean the medication isn't right for you. The 2.5 mg dose is an adjustment dose designed to help your body adapt, and significant weight loss typically happens at higher doses. This guide explains what to expect at the starting dose, why dose titration matters, and when to discuss concerns with your prescriber or GP.
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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.
Understanding Mounjaro Dose Titration and Expectations
The 2.5 mg dose is not the therapeutic dose. Mounjaro works through a process called dose titration, where you increase the dose every 4 weeks until reaching an effective level. Clinical data shows that meaningful weight loss typically occurs at 5 mg and above, with average losses of 15–21% of body weight achieved at higher doses (10–15 mg) over extended periods.
At the 2.5 mg starting dose, your body is adjusting to the medication. You may experience appetite reduction or changes in how full you feel, but significant weight loss in the first 4 weeks is uncommon. Many people taking tirzepatide (the active ingredient in Mounjaro) stay on their current dose for the full 4 weeks before increasing—this is standard practice in NHS tier 3 weight management services and private prescribing.
- Week 1–4: 2.5 mg adjustment phase—side effects may settle, appetite may reduce
- Week 5–8: Increase to 5 mg—weight loss typically becomes noticeable
- Week 9–12+: Further escalation if needed—greater weight loss expected
If you haven't had your dose reviewed after 4 weeks, contact your prescriber to discuss moving to the next dose level.
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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.
When to Worry and When to Be Patient
Some weight loss may take weeks to become visible, especially if you're only on the starting dose. However, contact your prescriber if: you've been on 2.5 mg for longer than 4 weeks with no dose increase scheduled; you have severe side effects preventing you from eating adequately; your KwikPen injection didn't feel like it worked (possible injection technique issue); or you have concerns about whether Mounjaro is right for you.
Your GP or prescriber may suggest checking your diet, physical activity level, and whether you're taking any other medications that might affect weight loss. Keep a food and weight log using a progress tracker to give your prescriber accurate information at your next review. Weight management medication works best alongside lifestyle changes—medication alone won't studied results.
- 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 2.5 mg Mounjaro supposed to cause weight loss?
The 2.5 mg dose is primarily an adjustment dose to help your body tolerate the medication. Weight loss is typically minimal at this dose. Noticeable results usually begin when you increase to 5 mg or higher. If you've been on 2.5 mg for 4 weeks, ask your prescriber about increasing to the next dose.
How long should I wait before deciding Mounjaro isn't working?
Give the medication at least 8–12 weeks at therapeutic doses (5 mg and above) before drawing conclusions. The first 4 weeks at 2.5 mg is just the adjustment phase. Combined with a reduced-calorie diet and increased physical activity, weight loss becomes clearer after several months. Track your progress using a weight loss progress tracker.
Can poor injection technique mean my Mounjaro isn't working?
Yes. If your injection didn't feel normal or you're unsure about technique, this could affect how the medication is absorbed. Your pharmacist or GP can show you the correct technique. Each KwikPen contains four doses—if one felt wrong, ensure the next one is injected correctly into the skin of your stomach, thigh, or upper arm.
Should I change my diet when starting Mounjaro?
Yes. Mounjaro works best alongside a reduced-calorie diet and increased physical activity. Even at 2.5 mg, you should be making dietary changes. Your prescriber may refer you to a dietitian through NHS tier 3 services, or suggest using food tracking. Use our free GLP-1 weight loss calculator to estimate projected results at your current and future doses.
What if I'm on 5 mg or higher and still not losing weight?
Contact your prescriber. They may increase your dose further, review your diet and exercise habits, check for other medications affecting weight loss, or discuss whether an alternative medication (such as Wegovy or other options) might suit you better. Individual response to tirzepatide varies 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.