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
Free tracker included with every download this week
What Is a 5mg Mounjaro Pen?
A 5mg Mounjaro pen is the first maintenance dose of tirzepatide after the initial 2.5mg starting phase. This KwikPen delivers a once-weekly injection that may help support weight management when combined with lifestyle changes. The 5mg dose is typically used for 4 weeks or longer before potentially increasing to 7.5mg, depending on individual response and tolerability. Understanding this dosing stage is important if you're considering or already using Mounjaro for weight management in the UK.
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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 the 5mg Dose Works in Your Treatment Plan
Mounjaro (tirzepatide) works as a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways that regulate appetite and blood sugar. At the 5mg dose, this mechanism may help you feel fuller after smaller meals, reduce food cravings, and slow how quickly food leaves your stomach.
- 5mg is the first maintenance dose after the initial 4-week 2.5mg starting phase
- It's taken as a once-weekly injection under the skin using a pre-filled KwikPen
- Clinical trial data shows participants on 5mg achieved approximately 15% average body weight loss over 72 weeks alongside reduced-calorie diet and physical activity
- You'll typically stay on 5mg for at least 4 weeks before your prescriber considers increasing to the next dose
- The pen contains 4 doses (4 weeks' supply) and must be stored in the refrigerator at 2–8°C
Individual results vary significantly based on diet, exercise, metabolism, and adherence. Always use the GLP-1 weight loss calculator on this page to explore potential outcomes at different doses, though these are estimates only.
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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.
Common Questions About the 5mg Mounjaro Dose
Many UK adults starting Mounjaro move from 2.5mg to 5mg after week 4. At this stage, side effects like nausea or stomach discomfort often begin to settle, though some people experience ongoing digestive changes. The 5mg KwikPen is identical in appearance to other Mounjaro doses—only the label indicates the strength.
If you're comparing Mounjaro to alternatives, note that Wegovy (semaglutide) has different dosing: it starts at 0.25mg and reaches a maximum of 2.4mg. The approximate 5mg Mounjaro equivalent is around 0.5mg Wegovy, though any switch between medications must be managed by your prescriber. Use our free BMI calculator to understand your baseline, and track progress with our free progress tracker throughout your 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 the 5mg Mounjaro pen available on the NHS in the UK?
Mounjaro is available through NHS specialist tier 3 weight management services for eligible adults, but availability and waiting times vary significantly by region. Private prescription through a GPhC-registered pharmacy is also an option without NHS referral, though this involves a cost. Your GP can discuss both pathways with you.
What should I do if I miss a 5mg Mounjaro injection?
If you remember within 4 days of your missed dose, take it as soon as possible and continue your normal weekly schedule. If more than 4 days have passed, skip that dose and take your next injection on the usual day. Never double-dose. Always maintain at least 72 hours between injections.
Can I move from 5mg Mounjaro to a higher dose?
Yes. Your prescriber will assess your progress and tolerability after at least 4 weeks on 5mg. If weight loss is progressing well and side effects are manageable, you may increase to 7.5mg. Dose increases happen gradually—typically 4 weeks at each level—to minimise side effects.
What are the most common side effects at the 5mg dose?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain. These often improve over time as your body adjusts. Less common but serious side effects include severe stomach pain (possible pancreatitis) or gallbladder problems. Report any concerning symptoms to your prescriber immediately.
How long should I stay on the 5mg dose?
You should remain on 5mg for at least 4 weeks to assess how well it's working and how your body tolerates it. If you're achieving good weight loss and managing side effects, your prescriber may recommend staying longer before increasing. Treatment duration depends on your individual response and health goals.
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.