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 Is 5mg Mounjaro and How Does It Work?
5mg is the first maintenance dose of Mounjaro (tirzepatide) prescribed in the UK after the initial four-week starting phase at 2.5mg. This dose represents the point where your body has adapted to the medication, and your prescriber assesses whether further increases are needed. Mounjaro is a prescription-only injection that activates two hormone pathways — GIP and GLP-1 — which may help regulate appetite and support weight management alongside diet and physical activity. Understanding what 5mg means and how it fits into your treatment journey is essential for setting realistic expectations.
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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.
5mg Mounjaro in the Treatment Schedule
Mounjaro is prescribed in a step-by-step dose escalation plan. The 2.5mg starting dose is given for the first four weeks, allowing your body to adjust and your GP or prescriber to monitor how you respond. After four weeks, if you're tolerating the medication well, you move to 5mg — the first true maintenance dose. You stay on 5mg for a minimum of four weeks (weeks 5–8) before any further increase. If needed, your prescriber may then escalate to 7.5mg, 10mg, 12.5mg, or the maximum of 15mg, with at least four weeks between each increase. This gradual approach helps minimise side effects and allows your body to adapt. Clinical data suggests that on 5mg, participants in the SURMOUNT trial experienced an average weight loss of approximately 15% of their body weight over 72 weeks, though individual results vary significantly. Your prescriber will assess whether 5mg is your ideal maintenance dose or whether you need to increase further based on your progress and tolerance.
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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 What to Expect at 5mg
At the 5mg dose, side effects are generally similar to the 2.5mg starting dose but may persist or evolve as your body continues to adjust. The most common side effects include nausea, diarrhoea, constipation, and reduced appetite — these typically reduce over time as your body adapts to tirzepatide. Some people experience injection site reactions (redness or mild bruising), headache, or fatigue. Most side effects are mild to moderate and manageable. However, if you experience severe stomach pain, persistent vomiting, signs of gallbladder problems, or serious allergic reactions, seek urgent medical advice. Your prescriber may recommend dietary adjustments or anti-nausea medication if side effects are troublesome. Use our free GLP-1 weight loss calculator to track your projected progress and our progress tracker to log your journey and monitor how you're responding to treatment.
- 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 5mg the standard dose for everyone on Mounjaro?
No. 5mg is the first maintenance dose, but many people increase beyond this. Your prescriber will assess whether 5mg is right for you or whether you need to escalate to 7.5mg, 10mg, or higher based on your progress, side effects, and clinical response over four weeks.
How long do you stay on 5mg Mounjaro?
You remain on 5mg for a minimum of four weeks (weeks 5–8 of treatment). After this period, if weight loss is progressing well and side effects are acceptable, your prescriber may increase your dose. Some people continue on 5mg long-term if it provides the desired result with tolerable side effects.
Can I get 5mg Mounjaro on the NHS in the UK?
Mounjaro is approved for NHS use within tier 3 specialist weight management services, but availability varies by region and ICB. Access typically requires a GP referral to a specialist service. Private prescription is available through UK-licensed prescribers and GPhC-registered pharmacies without NHS referral.
What's the difference between 5mg Mounjaro and 5mg Wegovy?
Mounjaro (tirzepatide) and Wegovy (semaglutide) are different medications with different dosing schedules. 5mg Mounjaro is not directly comparable to any single Wegovy dose. Approximate equivalence suggests 5mg Mounjaro ≈ 0.5–1mg Wegovy, but only your prescriber can advise on switching between them.
Will I lose weight on 5mg Mounjaro?
Clinical trials showed average weight loss of approximately 15% body weight at 5mg over 72 weeks, alongside reduced-calorie diet and physical activity. However, individual results vary significantly — some people lose more, some less. Use our GLP-1 weight loss calculator to estimate your potential progress based on your starting weight and dose.
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.