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 Your 2.5mg Mounjaro Might Not Be Working Yet
If you've started 2.5mg Mounjaro and feel it's not working, you're likely in the early titration phase — and this is completely normal. Mounjaro starts at a low dose for a reason: to allow your body to adjust and minimise side effects. Most people don't stay on 2.5mg for weight loss results; it's a stepping stone. Understanding when to expect results, what dose adjustments mean, and your UK access options can help you decide whether to continue, increase your dose, or explore alternatives like Wegovy.
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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 Mounjaro Dosing and Timing Expectations
The 2.5mg dose is an initiation dose only. It's designed to help your body adapt to tirzepatide, not to deliver significant weight loss. You typically stay on 2.5mg for 4 weeks, then increase to 5mg, and continue escalating every 4 weeks if tolerated — up to a maximum of 15mg once weekly via a Mounjaro KwikPen.
Timeline for noticing results: Most people don't see meaningful weight loss until reaching the 5mg, 7.5mg, or 10mg doses. Clinical trials showed that at 15mg, participants lost an average of 20.9% of body weight — but this took 72 weeks alongside diet and exercise. Results vary significantly between individuals.
- Weeks 1–4 at 2.5mg: expect adjustment, possible nausea, no significant weight loss
- Weeks 5–8 at 5mg: appetite reduction may begin; modest weight change possible
- Weeks 9–16 at 7.5–10mg: more noticeable appetite suppression; clearer weight loss trajectory
If you've been on 2.5mg for 4 weeks and tolerated it well, your prescriber should increase your dose. If you've only just started, give it the full 4 weeks before evaluating effectiveness.
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.
UK Cost, Access Routes, and Switching Alternatives
Private UK route: A single Mounjaro KwikPen (4 weeks supply at one dose) costs between £129–£320 depending on your dose and provider. Starting at 2.5mg is affordable, but monthly costs increase as you escalate. This is why some people explore whether Wegovy — a GLP-1 agonist alternative with different pricing — might suit them better, or whether they should pursue NHS access instead.
NHS access: If you're eligible (BMI 30+, or 27+ with weight-related health conditions), you can ask your GP for referral to a specialist tier 3 weight management service. NHS tirzepatide is now approved by NICE, but waiting times and availability vary significantly by region. There is no cost if approved via NHS.
Online prescription process: Private prescriptions typically require a 10–15 minute online clinical assessment with a UK-licensed prescriber. You'll be asked about your medical history, current medications, and whether you meet eligibility criteria. If approved, a prescription is issued to a registered pharmacy and your KwikPen is delivered within 2–3 days.
If 2.5mg truly isn't working after 4 weeks and you've tolerated it well, the next step is dose escalation to 5mg — not abandoning the medication. However, if you're experiencing significant side effects or cost concerns, discuss alternatives with your prescriber. Some people find Wegovy (semaglutide) more affordable or easier to tolerate, though efficacy varies individually. Use our free GLP-1 weight loss calculator to compare projected weight loss across different doses and medications — this can help you discuss realistic timelines with your prescriber. You can also track your progress using our free progress tracker to monitor subtle changes you might not otherwise notice over the first 4–8 weeks.
- 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 cause weight loss?
No — 2.5mg is an initiation dose only, designed for your body to adjust to tirzepatide, not for weight loss results. Weight loss typically begins at 5mg or higher. You'll stay on 2.5mg for 4 weeks before escalation. Give it the full 4 weeks, then discuss increasing your dose with your prescriber if you've tolerated it well.
How much does Mounjaro cost per month in the UK privately?
Private UK costs range from approximately £129–£320 per month depending on your dose. The starting 2.5mg dose is at the lower end; costs increase as you escalate to 5mg, 10mg, and 15mg. NHS access is free if you're eligible and referred through your GP to a specialist weight management service.
What's the difference between Mounjaro and Wegovy for UK weight loss?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist; Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials showed Mounjaro produced slightly greater average weight loss (20.9% vs 14.9%), but individual results vary. Both are prescription-only and priced similarly in the UK private market.
Can I get Mounjaro on the NHS if I can't afford it privately?
Yes — if you meet eligibility criteria (BMI 30+, or 27+ with weight-related health conditions), ask your GP for referral to a tier 3 specialist weight management service. NICE has approved tirzepatide for NHS use, though waiting times and regional availability vary. There is currently no cost if approved via NHS.
When should I switch from Mounjaro to something else if it's not working?
Don't switch immediately if you're on 2.5mg — this dose isn't therapeutic. Discuss dose escalation with your prescriber first. If you reach a higher dose (10mg+) and still see no appetite change or weight loss after 8–12 weeks, then discuss alternatives like Wegovy or reassessing your suitability for GLP-1 medication.
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.