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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What's the Difference Between 2.5mg and 5mg Mounjaro?
If you've been prescribed Mounjaro (tirzepatide) for weight management in the UK, you'll start on 2.5mg and typically move to 5mg after four weeks. These aren't fixed doses — they're part of a prescribed dose titration schedule. The 2.5mg starting dose allows your body to adjust to the medication, whilst the 5mg maintenance dose is where most people see sustained weight loss benefits. Understanding the difference between these two doses helps you know what to expect from your treatment plan and why your prescriber structures your Mounjaro prescription this way.
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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 Mounjaro Dose Titration Works in the UK
Mounjaro is not prescribed at a fixed dose from the start. Instead, UK prescribers follow a strict dose titration schedule, gradually increasing your tirzepatide dose to let your body adapt and minimise side effects.
- Week 1–4 (2.5mg): Starting dose. Your body adjusts to the GLP-1/GIP receptor agonist mechanism. Nausea and appetite reduction are typically mild at this dose.
- Week 5–8+ (5mg): First maintenance dose. After four weeks minimum, you move to 5mg — the dose where most clinical benefit appears. This is where weight loss typically accelerates.
- Weeks 9+: If your prescriber assesses that further escalation is needed, you may progress to 7.5mg, 10mg, 12.5mg, or the maximum 15mg — but only after spending minimum four weeks on each dose.
Each dose increase happens only if you're tolerating the current dose well and your prescriber agrees. You cannot skip steps or jump directly to 5mg.
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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: 2.5mg vs 5mg Mounjaro
Most common Mounjaro side effects — nausea, diarrhoea, constipation, and stomach discomfort — tend to be milder on 2.5mg than 5mg. The 2.5mg dose gives your digestive system time to adjust. When you move to 5mg, some people experience an increase in side effect intensity, though this often settles over a few weeks as your body acclimatises.
If side effects at 5mg become intolerable, your prescriber may pause escalation or reduce the dose temporarily. Always report side effects honestly — your Mounjaro prescription is designed to be manageable, and adjustments can be made.
- 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.
Will I lose more weight on 5mg than 2.5mg Mounjaro?
Yes, clinical evidence suggests greater weight loss at 5mg and higher doses. Clinical trials showed approximately 15% average body weight loss at 5mg versus smaller losses at 2.5mg. However, individual results vary significantly. Weight loss also depends on diet, activity level, and how your body responds to tirzepatide. Use our GLP-1 weight loss calculator to project potential outcomes at different doses.
Why can't I start on 5mg Mounjaro instead of 2.5mg?
Starting on 5mg increases side effect risk and makes tolerability worse. The 2.5mg starting dose lets your body adjust to the medication's mechanism gradually. This four-week adaptation period reduces nausea and allows your digestive system to acclimatise. Prescribers follow this titration schedule because it leads to better long-term adherence and outcomes.
How long do I stay on 2.5mg before moving to 5mg?
You must take 2.5mg Mounjaro for a minimum of four weeks before escalating to 5mg. Your prescriber will assess how well you're tolerating the medication at your review before authorising the dose increase. If you're experiencing significant side effects, your prescriber may extend the 2.5mg period.
Is 5mg the maximum Mounjaro dose I'll be prescribed?
No. 5mg is the first maintenance dose, not the maximum. The Mounjaro KwikPen is available in doses up to 15mg, and UK prescribers may escalate you further if clinically appropriate. Maximum dose escalation depends on your individual response, tolerability, and weight loss progress. Your prescriber will discuss dose progression with you at each review.
What happens if I can't tolerate 5mg Mounjaro?
If 5mg causes unmanageable side effects, your prescriber can pause escalation or temporarily reduce your dose. Some people do well on 2.5mg long-term, and this is a valid treatment option if 5mg isn't tolerated. Never stop Mounjaro without prescriber guidance, and always report tolerability issues at your next review or sooner if symptoms are severe.
Ready to take control of your weight loss journey?
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