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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Understanding Your Mounjaro 2nd Dose in the UK
Your second Mounjaro injection marks an important step in your weight management journey. If you're prescribed tirzepatide (Mounjaro) through the NHS or privately in the UK, understanding your 2nd dose — including timing, what to expect, and how it fits into your dose escalation plan — is essential for safe and effective treatment. This guide covers NHS prescribing context, dose progression, and practical information for UK patients.
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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.
Mounjaro Dose Titration and Your 2nd Dose Schedule
Mounjaro is prescribed as a dose titration, meaning your dose increases gradually over weeks to allow your body to adjust and find your therapeutic dose. Your 2nd dose comes 7 days after your first injection and is typically still the 2.5 mg starting dose, not a higher dose.
The standard Mounjaro titration schedule in UK prescribing is:
- Week 1–4: 2.5 mg once weekly (doses 1–4)
- Week 5–8: 5 mg once weekly (doses 5–8)
- Week 9–12: 7.5 mg once weekly
- Week 13–16: 10 mg once weekly
- Week 17–20: 12.5 mg once weekly
- Week 21+: 15 mg once weekly (maximum)
Your prescriber will assess your progress and tolerability at each stage before increasing. Using our GLP-1 weight loss calculator can help you project potential outcomes at different dose levels.
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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 From Your 2nd Mounjaro Injection
By your 2nd dose, you may have experienced side effects from your first injection — nausea, digestive changes, or appetite suppression are common. Most UK patients find these effects settle within the first 4–7 days as your body adapts. Your 2nd dose is still 2.5 mg, so if side effects were manageable, they typically don't worsen. If side effects were severe, contact your prescriber before your 2nd dose.
Timing matters: inject your 2nd dose exactly 7 days after your first injection (for example, if you injected on Monday week 1, inject the following Monday). Check the injection site (stomach, thigh, or arm) — rotate to a different area for your 2nd dose to reduce skin irritation. Store your KwikPen according to guidance and dispose of the used pen safely.
- 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 my 2nd Mounjaro dose higher than my 1st dose?
No. Both your 1st and 2nd Mounjaro doses are 2.5 mg. You remain on 2.5 mg for the first 4 weeks (4 injections). Your dose only increases to 5 mg in week 5 if your prescriber confirms you're tolerating treatment well. Never increase your dose without prescriber guidance.
Can I skip my 2nd dose if I had bad side effects from the 1st?
Do not skip without speaking to your prescriber first. Most side effects settle by day 5–7. Contact your GP or prescriber immediately if you experienced severe reactions. They may adjust your approach, but stopping abruptly isn't usually recommended. Side effect management strategies are available.
How do I know I've had my 2nd dose correctly?
Your 2nd dose is correct if: you injected 2.5 mg exactly 7 days after your 1st injection, you rotated your injection site, and you stored the pen correctly before use. Use our progress tracker to record your injection date and any side effects for reference at future appointments.
Will my 2nd dose help me lose weight?
Weight loss typically becomes noticeable after 4–8 weeks of consistent Mounjaro use, not from one or two doses. Your 2nd dose is part of building up the medication in your system. Clinical trials showed meaningful weight loss occurs over weeks and months, alongside a reduced-calorie diet and physical activity, with individual results varying considerably.
How do I get my 2nd Mounjaro dose on the NHS in the UK?
If you're prescribed Mounjaro through NHS tier 3 specialist weight management services, your prescriber will provide your full 4-week supply (4 KwikPens) at your initial appointment or through your pharmacy. Your 2nd dose is collected with your 1st. If you're using private prescribing, your pharmacy will supply all 4 pens together at the start of your treatment.
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.