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 Pen — What You Need to Know
The Mounjaro 5 mg pen is a prescription-only injection containing tirzepatide, used in the UK for weight management in eligible adults. It's the first maintenance dose most people reach after starting on the lower 2.5 mg starter dose. Each KwikPen contains four weekly doses and is part of a stepped dosing schedule where your prescriber may increase the dose gradually based on your individual response. This guide explains how the 5 mg dose works, what to expect, and how it fits into the Mounjaro treatment pathway in the UK.
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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 the Mounjaro 5 Mg Dose Works in Your Body
Mounjaro 5 mg is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways in your body. This dual action is what sets tirzepatide apart from other weight loss injections like Wegovy, which is a GLP-1 agonist only. At the 5 mg dose, Mounjaro works by:
- Reducing appetite and food cravings
- Helping you feel fuller after smaller meals
- Slowing how quickly food leaves your stomach
- Supporting healthier fat utilisation
- Helping regulate blood sugar levels
Clinical trials showed that people on 5 mg Mounjaro lost an average of approximately 15% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity. However, individual results vary significantly — some people see greater weight loss, others more modest results. The 5 mg dose is typically a first maintenance dose; your prescriber may increase it further if needed based on your response and tolerance.
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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 5 Mg Pen — What to Expect and Getting Started
Each Mounjaro KwikPen contains enough medication for four once-weekly injections, so a 5 mg pen lasts four weeks. You inject under the skin (subcutaneously) once per week, typically on the same day each week. Common injection sites include the stomach, upper thigh, or upper arm. Most people start on the 2.5 mg dose for the first four weeks to allow their body to adjust, then move to 5 mg. If you experience manageable side effects like nausea or mild stomach discomfort, these often ease over time.
To access Mounjaro in the UK, you'll need a prescription from a licensed prescriber following a clinical assessment. You can use our free GLP-1 weight loss calculator to estimate potential weight loss at different Mounjaro doses. Your prescriber will consider your BMI, health conditions, and other medications before prescribing, and will monitor your progress regularly.
- 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 the Mounjaro 5 mg pen the maximum dose?
No. The 5 mg pen is typically the first maintenance dose. Your prescriber may gradually increase you to 7.5 mg, 10 mg, 12.5 mg, or the maximum 15 mg dose depending on your individual response, tolerance, and weight loss progress. Dose escalation is gradual, with a minimum of four weeks at each dose before increasing.
How much does a Mounjaro 5 mg pen cost in the UK?
Costs vary between providers. Private prescriptions typically range from £129–£320 per month depending on the dose and pharmacy. NHS access is through specialist tier 3 weight management services where available, though waiting lists vary by region. Contact your prescriber or local weight management service for specific pricing or NHS eligibility.
Can I switch between Mounjaro and Wegovy?
Switching between Mounjaro (tirzepatide) and Wegovy (semaglutide) is possible but requires prescriber guidance. Whilst approximate dose equivalences exist — for example, 5 mg Mounjaro is roughly equivalent to 0.5 mg Wegovy — any switch must be managed by a healthcare professional. Your prescriber will consider your response and individual circumstances.
What are the common side effects of Mounjaro 5 mg?
The most common side effects include nausea, diarrhoea, constipation, and stomach discomfort. These are typically mild to moderate and often improve over time as your body adjusts. Serious side effects are rare but include severe stomach pain (possible pancreatitis) or serious allergic reactions. Report any concerning symptoms to your prescriber immediately.
Do I need a clinical assessment before getting a Mounjaro 5 mg prescription?
Yes. Mounjaro is prescription-only and requires a clinical assessment from a UK-licensed prescriber before you can receive it. Your prescriber will check your BMI, health history, current medications, and whether you're eligible based on NICE guidelines. This ensures the medication is safe and appropriate for you personally.
Ready to take control of your weight loss journey?
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