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 in Week 2 of Mounjaro Treatment?
Week 2 of Mounjaro (tirzepatide) is when you'll administer your second 2.5 mg injection as part of the standard dose titration schedule. This is the starting phase, and most people experience the initial side effects during this period. In the UK, whether you're accessing Mounjaro through NHS specialist weight management services or a private online prescription, understanding what to expect in week 2 helps you manage symptoms and stay on track with your treatment plan.
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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.
NHS Mounjaro Week 2: Eligibility and Starting Treatment
If you're in week 2 of Mounjaro through an NHS tier 3 specialist weight management service, you've already been assessed for eligibility. NHS guidance via NICE supports tirzepatide for adults with a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with at least one weight-related health condition such as type 2 diabetes, high blood pressure, or cardiovascular disease. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds.
Week 2 marks your second injection — still at the 2.5 mg starting dose. You'll remain on this dose for weeks 1–4 (four injections total) before escalation. This slow titration allows your body to adapt and helps your prescriber monitor how you're responding. NHS prescribing typically occurs in tier 3 services after referral from your GP, though waiting times vary significantly by region.
- 2.5 mg dose weeks 1–4
- Minimum 4 weeks before dose increase
- Clinical monitoring throughout titration
- Side effect management support from specialist team
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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 and Management in Week 2
By week 2, nausea is the most common side effect reported — affecting many people starting tirzepatide. You may also experience diarrhoea, constipation, stomach discomfort, or loss of appetite. These are typically mild to moderate and often reduce over time as your body adjusts. Never stop your injection without consulting your GP or specialist prescriber.
Practical management strategies: eat smaller, regular meals; stay hydrated; avoid fatty or greasy foods; and take ginger supplements if approved by your prescriber. Most people find symptoms settle by weeks 3–4 as the body acclimatises. If side effects are severe or persistent, contact your specialist team immediately — they may adjust your approach or provide additional support. Track your symptoms and weight progress using our free progress tracker to share with your healthcare team at your next review.
- 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 nausea in week 2 of Mounjaro normal?
Yes, nausea is very common in the first few weeks of tirzepatide, especially at the 2.5 mg starting dose. It typically improves by weeks 3–4 as your body adapts. Eating smaller meals, staying hydrated, and avoiding fatty foods can help. Contact your prescriber if nausea is severe or persistent.
Can I stop Mounjaro in week 2 if side effects are too much?
Do not stop without medical guidance. Contact your GP or specialist prescriber instead — they can provide management strategies, suggest dietary adjustments, or discuss whether continuing is right for you. Stopping abruptly without professional advice is not recommended.
Will I lose weight in week 2 of Mounjaro?
Weight loss is typically gradual and varies between individuals. Most people notice appetite reduction rather than immediate weight loss in week 2. Significant weight loss usually becomes apparent after 4–8 weeks as you progress through the dose escalation. Results depend on diet, activity level, and individual metabolism.
How do I access Mounjaro through the NHS in the UK?
Ask your GP for a referral to your local tier 3 specialist weight management service. These services assess your eligibility and manage tirzepatide prescribing. Availability and waiting times vary by region (ICB). Private online prescribing is also available without NHS referral if you prefer.
What's the difference between Mounjaro and Wegovy for NHS patients?
Both are prescription-only weight management injections available in the UK. Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist; Wegovy (semaglutide) is a GLP-1 agonist. Clinical trials showed Mounjaro may support slightly greater average weight loss, though results vary individually. Your prescriber will recommend based on your health profile.
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.