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 Happens at Your Mounjaro 2nd Dose?
Your second Mounjaro injection marks an important milestone in your weight management journey. The second dose typically occurs around week 5, when you step up from the starting dose of 2.5 mg to 5 mg. This dose escalation is a standard part of the titration schedule designed to help your body adjust gradually whilst building towards the maintenance dose. Understanding what to expect during this phase can help you feel more confident and prepared as your treatment progresses.
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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 2nd Dose Timing and Schedule
Your second Mounjaro injection arrives approximately 4 weeks after your first dose. The standard titration schedule works as follows:
- Weeks 1–4: First dose of 2.5 mg (one KwikPen)
- Weeks 5–8: Second dose of 5 mg (escalation)
- Weeks 9–12: Third dose of 7.5 mg (further escalation)
- Weeks 13–16: Fourth dose of 10 mg
Each dose is injected once weekly on the same day of the week. If you miss a dose by more than 4 days, skip it and return to your normal schedule. The minimum time between injections must be at least 72 hours (3 days). This gradual dose escalation — known as dose titration — allows your body to adapt to tirzepatide whilst minimising side effects. Many people tolerate the second dose better than the first as their digestive system has begun adjusting.
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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.
Side Effects at the 2nd Dose and What to Do
Some people experience reduced side effects by week 5, whilst others notice they persist or slightly intensify when the dose increases. Common experiences at the second dose include nausea, constipation, or mild stomach discomfort. These are usually temporary and tend to settle within a few days as your body adjusts to the higher dose of tirzepatide.
If side effects are severe or concerning, contact your GP or prescriber immediately. Do not skip doses or stop treatment without medical advice. Your prescriber may recommend strategies like dietary adjustments or temporarily remaining on 5 mg for longer than 4 weeks before progressing to 7.5 mg. Use our GLP-1 weight loss calculator to track your projected progress across all dose levels, and our progress tracker to log any side effects you experience alongside your weight and wellbeing.
- 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.
When exactly do I take my second Mounjaro dose?
Your second dose is due approximately 4 weeks after your first injection. Inject it on the same day of the week, at roughly the same time. If you miss your second dose window by more than 4 days, skip that dose and resume your normal schedule the following week.
Will my second Mounjaro dose be stronger in terms of side effects?
Not necessarily. Many people find side effects ease by week 5 as their body adapts. However, the dose increase from 2.5 mg to 5 mg may cause temporary nausea, constipation, or stomach discomfort. These typically resolve within a few days. Staying hydrated and adjusting your diet can help.
Can I stay on 2.5 mg instead of progressing to 5 mg?
Potentially, yes — but only under your prescriber's guidance. The standard titration schedule progresses to 5 mg after 4 weeks, but if you experience significant side effects, your prescriber may recommend remaining on 2.5 mg for longer. Always discuss concerns with your GP or prescriber before making changes.
How much weight should I have lost by my second dose?
Weight loss varies significantly between individuals. At 4 weeks, most people are only just beginning their weight loss journey. Don't judge the medication's effectiveness until you've reached a stable maintenance dose (typically 10 mg or higher). Our GLP-1 weight loss calculator can help you understand realistic timelines.
Is the second dose the same medication as the first, just a higher amount?
Yes. Both injections contain tirzepatide — the active ingredient in Mounjaro. Your second dose KwikPen contains a higher concentration (5 mg vs 2.5 mg), allowing you to inject the same volume but receive double the medication. This gradual increase helps your body tolerate the treatment better.
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.