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's the Difference Between 2.5mg and 5mg Mounjaro?
The main difference between 2.5mg and 5mg Mounjaro (tirzepatide) is their role in your treatment journey. The 2.5mg dose is the standard starting dose used for the first four weeks, whilst 5mg is the first maintenance dose you'll typically move to after your initial titration period. Both are prescription-only medicines requiring clinical assessment, and your prescriber will determine which dose is appropriate based on your individual health, BMI, and response to treatment. Understanding the dose progression is key to getting the most from your weight management plan.
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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.
2.5mg vs 5mg — Role and Timing in Your Treatment
2.5mg Mounjaro is the starting dose for all adults beginning tirzepatide treatment. You'll inject 2.5mg once weekly for four weeks to allow your body to adjust to the medication. During this phase, your GP or prescriber monitors your tolerance and response. Many people experience mild nausea or digestive changes during week one, which typically improve as your body adjusts.
5mg Mounjaro is the first maintenance dose, introduced after four weeks at 2.5mg. This dose is where most people stabilise and see meaningful weight loss effects. Clinical trials (SURMOUNT-1) showed that participants on 5mg lost an average of approximately 15% of their body weight over 72 weeks, though individual results vary significantly.
Your prescriber may keep you on 5mg if it's working well for your weight loss goals, or they may increase further depending on your progress and tolerance. The Mounjaro KwikPen device contains four pre-filled pens (four weeks' supply), so each refill represents your current 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.
Side Effects and Tolerability — Does Dose Matter?
Side effect severity can differ between 2.5mg and 5mg, though individual experience varies. Common side effects like nausea, vomiting, and diarrhoea are most noticeable in week one on 2.5mg and typically ease within days as your body adapts. When you increase to 5mg, some people experience mild side effects again, but these usually settle within a few days.
Serious side effects (severe stomach pain, gallbladder problems, severe allergic reactions) are rare at both doses but require immediate medical attention. If you experience severe or persistent side effects at 2.5mg, your prescriber may recommend staying at this dose longer or exploring alternatives. Your GP can assess your individual tolerability and adjust your plan accordingly.
- 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.
How long do I stay on 2.5mg Mounjaro before moving to 5mg?
You take 2.5mg for exactly four weeks (one Mounjaro KwikPen worth of injections). After four weeks, assuming you're tolerating it well, your prescriber will move you to 5mg. If you're having significant side effects, your prescriber may recommend staying on 2.5mg longer before escalating.
Is 5mg Mounjaro more effective for weight loss than 2.5mg?
5mg typically produces better weight loss results than 2.5mg. Clinical trial data showed participants on 5mg lost approximately 15% body weight on average. However, some people achieve their weight loss goals on 5mg and don't need further dose increases. Results vary individually based on diet, activity, and metabolism.
Can I stay on 2.5mg Mounjaro long-term if it's working for me?
Yes, if you're seeing good weight loss progress on 2.5mg and tolerating it well, your prescriber may keep you on this dose. There's no requirement to escalate doses if your goals are being met. Treatment is personalised based on your individual response and health status.
What's the difference between Mounjaro and Wegovy doses?
Mounjaro (tirzepatide) and Wegovy (semaglutide) have different dose ranges and mechanisms. Mounjaro starts at 2.5mg and goes up to 15mg weekly. Wegovy starts at 0.25mg and maxes at 2.4mg weekly. Mounjaro is a dual GIP+GLP-1 agonist, whilst Wegovy is GLP-1 only. Both require prescription and clinical assessment in the UK.
Will my prescriber tell me which dose is right for me?
Yes. Your GP or weight management prescriber will assess your eligibility based on your BMI, health conditions, and medical history. They'll start you on 2.5mg and review your progress after four weeks before deciding whether to increase to 5mg. They consider your side effects, weight loss results, and overall health. Use our free GLP-1 weight loss calculator to get a rough estimate of potential outcomes at different doses. ```
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.