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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Mounjaro 5mg — UK Dosage Information
Mounjaro 5mg is the first maintenance dose of tirzepatide, a prescription-only GIP and GLP-1 receptor agonist injection licensed in the UK for weight management. After starting at 2.5mg for four weeks, adults typically progress to the 5mg dose as part of their personalised treatment plan. This page explains what the 5mg dose is, how it works, and what to expect from this stage of treatment.
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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.
What Is Mounjaro 5mg and How Does It Work?
Mounjaro 5mg is delivered once weekly via a pre-filled KwikPen injection device. At this dose, the medication activates both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 receptor pathways, which distinguishes tirzepatide from other weight loss injections like semaglutide (Wegovy). This dual mechanism works by reducing appetite, increasing feelings of fullness after smaller meals, and supporting more regulated blood sugar responses.
- You remain on 5mg for a minimum of four weeks before any potential dose increase
- The injection is given into the stomach, thigh, or upper arm
- Each pre-filled pen contains four weekly doses (one month's supply)
- Storage: refrigerate unopened pens at 2–8°C; after first use, store at room temperature (below 30°C) for up to 30 days
- Most people experience side effects reducing after the first few weeks at each dose level
Individual response to the 5mg dose varies — some people see significant weight loss; others may need to progress to higher doses (7.5mg, 10mg, or more) for optimal results.
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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.
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Mounjaro 5mg — UK Eligibility and Prescription
In the UK, Mounjaro is prescription-only and available through NHS specialist weight management services or private prescribers following a clinical assessment. You may be eligible if you have a BMI of 30 or above, or BMI 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease.
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply. Your GP or prescriber will assess whether tirzepatide is suitable for you individually. Use our free BMI calculator and GLP-1 weight loss calculator above to understand your starting point and project potential outcomes at different doses.
- 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 Mounjaro 5mg a starting dose?
No. Mounjaro starts at 2.5mg for four weeks, then escalates to 5mg as the first maintenance dose. Your prescriber may keep you on 5mg or continue escalating based on your weight loss response and tolerance.
How much weight loss can I expect on Mounjaro 5mg?
Clinical trials showed average weight loss of approximately 15% body weight on the 5mg dose. Individual results vary significantly depending on diet, physical activity, and personal response. Faster results are not assured — sustainable weight loss is the aim.
What are the most common side effects at Mounjaro 5mg?
Nausea, diarrhoea, constipation, and stomach pain are very common, particularly when first starting or increasing doses. These typically reduce within days to weeks as your body adjusts. Seek medical attention for severe or persistent stomach pain.
Can I skip a dose or stop Mounjaro 5mg?
If you miss a dose by less than four days, take it as soon as remembered and continue your normal schedule. If more than four days have passed, skip that dose and take your next one as planned. Do not double-dose. Always discuss stopping with your prescriber.
How is Mounjaro 5mg different from Wegovy or Saxenda?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, whilst Wegovy (semaglutide) is a GLP-1-only agonist, and Saxenda (liraglutide) is a daily injection rather than weekly. Dual-action may offer different results — clinical trials suggest tirzepatide may support greater average weight loss, though individual outcomes vary.
Ready to take control of your weight loss journey?
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