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 to Expect After 30 Days on Mounjaro
After 30 days on Mounjaro (tirzepatide), most people are still in the initial adjustment phase. You'll typically be on the 2.5 mg starting dose during this first month, which is designed to help your body adapt to the medication. At this stage, you may experience nausea or other side effects, but significant weight loss isn't expected yet — clinical trials showed meaningful results emerge over weeks 5–12 as doses increase. This guide explains what's normal after your first month on this prescription weight loss injection.
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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.
Effects and Side Effects After 30 Days
In your first 30 days on Mounjaro, you're receiving the 2.5 mg starting dose — a low strength specifically chosen to allow your body to adjust. Most people report nausea as the most common side effect during this phase, though it often improves as you continue. You may also experience changes in appetite, mild diarrhoea or constipation, and stomach discomfort.
Weight loss at 30 days is typically minimal or absent — this is completely normal. Clinical trials showed that real weight loss momentum builds from week 5 onwards as your dose increases to 5 mg and beyond. Some people report feeling fuller after meals or reduced food cravings, but others notice little change at this stage.
If side effects are severe or not improving, contact your prescriber. They may adjust your timing of injections, dietary advice, or consider dose management strategies. After 30 days, your next step is dose escalation to 5 mg (week 5) if you've tolerated the 2.5 mg injection well.
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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 Prescribing, Dose Titration, and Next Steps
If you received Mounjaro through NHS tier 3 specialist weight management services, you'll follow their specific monitoring schedule. The NHS recommends assessing side effects and tolerability at each 4-week interval before increasing your tirzepatide dose. At 30 days, your NHS team will prepare you for the step to 5 mg at week 5.
For those prescribed through private UK prescribing services, the same dose titration schedule applies. Never skip to a higher dose — spending at least 4 weeks on each strength helps your body adjust and allows your prescriber to monitor your response.
Track your progress during this period using our free progress tracker, which helps you log any side effects, appetite changes, or early signs of weight loss. This information is valuable to share with your prescriber at your next review. Mounjaro vs Wegovy — if you're comparing treatments — both follow similar 4-week escalation schedules, though starting doses differ.
- 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 it normal to have no weight loss after 30 days on Mounjaro?
Yes, completely normal. The 2.5 mg starting dose is designed for tolerance, not weight loss. Clinical trials showed meaningful weight reduction begins at week 5–8 as doses increase. If you've tolerated the injection well, your prescriber will escalate to 5 mg at week 5.
What side effects should I expect in the first 30 days?
Nausea is most common, followed by changes in appetite, diarrhoea, constipation, and stomach discomfort. Most people find nausea improves with time. If side effects are severe, contact your prescriber — they can suggest timing adjustments or dietary changes.
How does the NHS dose titration work for Mounjaro?
The NHS follows a 4-week escalation schedule: 2.5 mg (weeks 1–4), then 5 mg (weeks 5–8), and beyond. Your tier 3 specialist service will assess your tolerability and response before each increase. This structured approach ensures safety and effectiveness.
Should I change my diet or exercise in the first 30 days?
Yes. Mounjaro works best alongside a reduced-calorie diet and increased physical activity from day one. You don't need to wait for weight loss to begin — healthy changes now support better results as your dose increases. Our GLP-1 weight loss calculator can help you estimate your potential progress.
What happens if I can't tolerate the 2.5 mg dose?
Contact your prescriber immediately. They may suggest staying on 2.5 mg longer, adjusting injection timing, dietary modifications, or in rare cases, considering whether Mounjaro is suitable for you. Do not increase your dose without medical guidance.
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.