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 5 mg Injection: NHS UK Information
Mounjaro 5 mg is the first maintenance dose for adults prescribed this weekly weight loss injection in the UK. This dose is reached after four weeks on the starting dose of 2.5 mg. At this point, your body has adjusted to the medication, and 5 mg becomes your regular maintenance injection — though your prescriber may increase it further depending on your individual response and health goals. Understanding what happens at the 5 mg stage helps you know what to expect as you progress through your 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.
NHS Eligibility and How the 5 mg Dose Fits In
In the UK, Mounjaro (tirzepatide) is a prescription-only, once-weekly injectable that activates two natural hormone pathways — GIP and GLP-1 — which help regulate appetite and support weight management. The 5 mg dose is reached in week 5 after starting on 2.5 mg for four weeks. This is where most people settle into their regular treatment schedule, though your dose may be increased further based on clinical response.
NHS eligibility criteria:
- BMI of 30 kg/m² or above, OR
- BMI of 27–29.9 kg/m² with at least one weight-related health condition (type 2 diabetes, prediabetes, high blood pressure, sleep apnoea, cardiovascular disease, or abnormal blood fats)
- For South Asian, Chinese, Black African, or Black Caribbean adults: thresholds may be lower (BMI 27.5 or above), reflecting higher health risks at lower weights
- Adults aged 18 and over
Access via NHS specialist tier 3 weight management services requires a referral from your GP. Waiting times and availability vary significantly by region, with some areas having longer waiting lists than others.
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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
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What to Expect at 5 mg and NHS Support
Once you reach the 5 mg dose, you'll continue this injection once weekly unless your prescriber recommends escalating further (to 7.5 mg, 10 mg, 12.5 mg, or 15 mg maximum). Clinical trial data shows that at 5 mg, Mounjaro supports approximately 15% average body weight loss — though individual results vary significantly. Combined with a reduced-calorie diet and increased physical activity, this dose helps many people feel fuller longer and reduce food cravings.
Side effects at 5 mg are typically nausea, constipation, diarrhoea, or stomach discomfort — most people find these settle within 2–3 weeks as their body adjusts. Your NHS specialist team will monitor your progress at regular appointments and adjust your dose or support based on your individual response. Use our free GLP-1 weight loss calculator to estimate potential progress at 5 mg and higher 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 5 mg available on the NHS?
Yes, Mounjaro (tirzepatide) is approved for NHS use and can be prescribed by specialist tier 3 weight management services following NICE guidance. Access requires a GP referral to your local specialist service. Availability and waiting times vary by region. Private online prescribing is also available if you prefer to access it outside the NHS.
How much weight will I lose at 5 mg?
Clinical trials showed that at 5 mg, Mounjaro supports an average body weight loss of approximately 15% — though individual results vary significantly. Some people see more loss, others less. Weight loss depends on your starting weight, adherence to a reduced-calorie diet, physical activity, and individual metabolism. Use our weight loss calculator to see personalised projections.
When do you move from 5 mg to a higher dose?
Your prescriber will assess your progress and response after 4 weeks on the 5 mg dose. If weight loss is progressing well and you're tolerating the injection, you may remain on 5 mg. If additional support is needed, your dose may be increased to 7.5 mg and beyond, up to the maximum of 15 mg. This decision is individualised based on your clinical response.
What are the side effects at 5 mg?
Common side effects at 5 mg include nausea, diarrhoea, constipation, and stomach pain — these are reported in more than 1 in 10 people. Most side effects settle within 2–3 weeks as your body adjusts. Eating smaller meals, staying hydrated, and avoiding fatty foods can help. Speak to your prescriber if side effects persist or cause concern.
How does Mounjaro at 5 mg compare to Wegovy?
Mounjaro (tirzepatide) at 5 mg is a dual GIP+GLP-1 agonist, whilst Wegovy (semaglutide) at equivalent doses acts on GLP-1 alone. Clinical trials suggest Mounjaro may produce slightly greater average weight loss, but results vary between individuals. The choice depends on NHS availability in your area, clinical assessment, and personal factors — your GP or prescriber can advise which is most appropriate for you. ```
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