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 Second Dose — UK Guide to Dose Escalation
Your second Mounjaro dose is part of the standard dose titration schedule in the UK. After your initial 2.5 mg starting dose, you'll continue with the same dose for a full four weeks before any escalation is considered. Understanding what to expect from your second week of treatment, including side effects and injection timing, helps you prepare for your weight management journey. Your prescriber will monitor your response before adjusting your Mounjaro KwikPen dose further.
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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.
Understanding Mounjaro Dose Escalation in the UK
Your second Mounjaro dose is administered exactly one week after your first injection, using the same 2.5 mg strength. The UK prescribing protocol requires you to remain on this starting dose for a minimum of four weeks before escalation, even if you tolerate it well. This allows your body to adjust to tirzepatide and gives your prescriber time to assess how you're responding.
The second injection follows the same process as the first: use a fresh KwikPen (which contains four doses), inject into your stomach, upper thigh, or upper arm, and rotate your injection site weekly. After your second dose, common side effects like nausea or changes in appetite may persist or become more noticeable — this is expected and typically reduces over time.
- Keep your KwikPen refrigerated between doses (2–8°C)
- After first use, you can store at room temperature for up to 30 days
- Mark your calendar for your third dose exactly one week later
- Report any severe side effects to your prescriber immediately
Many people find side effects peak around weeks 2–3 and then settle. If side effects are severe, contact your GP or prescriber — they may advise pausing escalation or managing symptoms differently.
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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.
NHS Access and Prescription Timing for Mounjaro
In the UK, Mounjaro is available through NHS specialist tier 3 weight management services or via private prescribing. Whether you receive your second dose depends on your access route. If you're prescribed through the NHS, your specialist service will manage your dose schedule and monitor your progress at each escalation point.
Patients accessing Mounjaro privately will receive their prescription following an online clinical assessment. Your prescriber will confirm you're suitable to continue to your second dose and beyond. It's important to keep track of your injection dates — missing or delaying doses can affect results. If you miss a dose, contact your prescriber for guidance; if it's been fewer than four days, you can usually take it as soon as remembered.
Use our free GLP-1 weight loss calculator to project your potential weight loss trajectory across different dose levels, and our BMI calculator to track your progress from week to week.
- 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.
Can I skip to a higher dose instead of taking my second 2.5 mg injection?
No. UK prescribing guidelines require a minimum four-week period on 2.5 mg before dose escalation, even if you tolerate the starting dose well. This allows your body to adjust safely and gives your prescriber adequate time to assess your response and side effects before any increase.
Will side effects be worse with my second Mounjaro dose?
Not necessarily. Many people find side effects remain similar to their first dose or gradually improve over weeks 2–4. Some experience peak side effects around week 2–3, then notice improvement. If side effects worsen significantly, contact your prescriber — they may recommend symptom management strategies or monitor you more closely before escalating.
What if I can't take my second dose on schedule?
If you miss your second dose, take it as soon as you remember if it's been fewer than four days. If more than four days have passed, skip it and take your next scheduled dose on your normal day. Never take two doses within 72 hours. Contact your prescriber if you're unsure.
How do I know if my second Mounjaro dose is working?
Early signs include reduced appetite, feeling fuller after smaller meals, and less interest in foods you usually enjoy. Weight loss typically appears around week 3–4 at the earliest. Your prescriber may ask about appetite changes and take your weight at follow-up appointments. Use our progress tracker to log your weight weekly and spot trends over time.
Is there a difference between my second dose and future escalations?
Your second dose is the same as your first — both are 2.5 mg. Real escalation begins at week 5 when you may move to 5 mg (if tolerated and appropriate). Each subsequent dose increase follows similar four-week monitoring periods. Your prescriber will decide escalation based on your individual response, side effects, and weight loss progress.
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.