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
What Is 2.5mg Mounjaro?
2.5mg is the standard starting dose of Mounjaro (tirzepatide), a prescription-only weight management injection licensed in the UK. This initial dose is used during weeks 1–4 of treatment to help your body adjust to the medication. It's not the dose you'll stay on long-term — your prescriber will increase it gradually every 4 weeks depending on your tolerance and how well you're responding. Understanding the dose titration process helps set realistic expectations for your weight loss journey.
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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.
How the 2.5mg Starting Dose Works
Mounjaro is a dual GIP and GLP-1 receptor agonist, which means it activates two natural hormone pathways that regulate appetite and food intake. At 2.5mg, you're receiving a lower dose designed to let your body adapt to the medication gradually and minimise initial side effects.
During the first 4 weeks on 2.5mg, the medication begins working to:
- Reduce appetite and food cravings
- Help you feel fuller after smaller meals
- Slow how quickly food leaves your stomach
- Support better blood sugar control
Most people experience some nausea or digestive changes during this adjustment period — this often improves as your body adapts. After 4 weeks, your prescriber will increase your dose to 5mg if you're tolerating 2.5mg well. This dose titration continues until you reach an effective maintenance dose, typically between 5–15mg.
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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.
What to Expect on 2.5mg Mounjaro
On the 2.5mg starting dose, you're unlikely to see dramatic weight loss in the first 4 weeks — the primary goal at this stage is safety and tolerability. However, many people do report initial benefits: reduced appetite, fewer food cravings, and less interest in sugary or fatty foods. Common side effects at this dose include nausea, mild constipation or diarrhoea, and reduced appetite (which is intentional).
You'll receive 4 injections (one per week) in a KwikPen device. Store unopened pens in the fridge at 2–8°C. You can inject into your stomach, upper thigh, or upper arm, rotating the injection site each week. Keep a record of your weight and how you're feeling — you can use our free progress tracker to log your journey. After 4 weeks, discuss your experience with your prescriber before moving to the 5mg dose.
- 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 enough for weight loss?
2.5mg is a starting dose, not a treatment dose. Clinical trials show meaningful weight loss typically occurs at higher doses (5–15mg). However, 2.5mg is important for safety — it lets your body adjust and helps your prescriber find the right dose for you. Most people need to reach at least 5mg for noticeable results.
How long do I stay on 2.5mg Mounjaro?
You take 2.5mg for exactly 4 weeks (4 injections). After that, if you're tolerating it well, your prescriber will increase you to 5mg. This gradual increase continues every 4 weeks, with the dose going up to 7.5mg, 10mg, 12.5mg, and finally 15mg if needed.
What are the side effects of 2.5mg Mounjaro?
Common side effects at the starting dose include nausea, mild diarrhoea or constipation, reduced appetite, and stomach discomfort. Most of these improve within 1–2 weeks as your body adapts. Serious side effects are rare but include severe stomach pain (seek urgent medical attention). Always report persistent side effects to your prescriber.
Can I buy 2.5mg Mounjaro without a prescription in the UK?
No — Mounjaro is prescription-only in the UK. You'll need a clinical assessment from a licensed prescriber before it can be prescribed. Access is through NHS specialist weight management services (long waiting lists in many areas) or private online prescribing via GPhC-registered pharmacies.
How does 2.5mg Mounjaro compare to Wegovy?
Mounjaro (tirzepatide) is a dual GIP+GLP-1 agonist, whereas Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials suggest Mounjaro may produce slightly greater weight loss at equivalent doses. However, Wegovy starts at 0.25mg (much lower), so early side effect profiles differ. Both require prescription and clinical assessment.
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.