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
First 24 Hours On Mounjaro — What You Need To Know
Starting Mounjaro (tirzepatide) is a significant step, but knowing what to expect in the first 24 hours helps you prepare properly. Your first injection is a 2.5 mg starting dose delivered via the pre-filled Mounjaro KwikPen, and understanding the cost, how to access it in the UK, and what happens after that initial dose can ease any concerns. Whether you're accessing Mounjaro through the NHS or privately, this guide covers everything you need to know about getting started safely and what to anticipate as your body adjusts.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
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.
UK Access Routes: NHS vs Private Prescription
In the UK, you can access Mounjaro (tirzepatide) through two routes: NHS specialist weight management services or private prescription through a licensed online prescriber. NHS access is available through NICE-approved tier 3 or 4 specialist weight management services, though availability and waiting times vary significantly by region and ICB (Integrated Care Board). Your GP can refer you to your local specialist service, but queues can be months or even years in some areas.
Private prescription offers faster access without an NHS referral. Following an online clinical assessment with a UK-licensed prescriber, you receive a prescription that a GPhC-registered pharmacy dispenses. Private costs typically range from £129–£320 per month depending on your dose, with the starting 2.5 mg dose at the lower end of this range. Many providers offer regular online check-ins to monitor your progress and adjust your dose as needed.
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.
Your First 24 Hours: What To Expect After Injection
Your first Mounjaro injection is a small 2.5 mg dose designed to help your body adjust to the medication. You'll inject once weekly at the same time each week—into your stomach, thigh, or upper arm using the pre-filled KwikPen. Most people experience mild nausea in the first 24 hours, though this often improves within days as your body adapts. Eat small, frequent meals and stay hydrated to help manage this.
Store your KwikPen in the fridge (2–8°C) if unopened, but once in use you can keep it at room temperature below 30°C for up to 30 days. If you experience severe stomach pain, difficulty breathing, or signs of allergic reaction (swelling of face or lips), seek medical attention immediately. Most side effects are mild and temporary, but your prescriber should be your first point of contact for any concerns.
- 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.
How much does Mounjaro cost in the UK privately?
Private Mounjaro costs typically range from £129–£320 per month depending on your dose. The starting 2.5 mg dose is usually at the lower end, increasing as you move through dose titration up to the maximum 15 mg. Prices vary between GPhC-registered pharmacies, so it's worth comparing options. Always ensure you're using a legitimate UK-licensed prescriber and pharmacy.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro is NICE-approved for NHS use through specialist tier 3 and 4 weight management services. You need a GP referral to your local specialist service. However, NHS availability and waiting times vary significantly by region—some areas have accessible services while others have very long waiting lists. Ask your GP about local options.
What happens in the first 24 hours after my first Mounjaro injection?
Your first 2.5 mg dose may cause mild nausea, which usually improves within a few days as your body adjusts. Eat small, frequent meals and drink plenty of water. Store your KwikPen in the fridge before use, then at room temperature below 30°C for up to 30 days. Contact your prescriber if you experience severe pain, difficulty breathing, or allergic symptoms.
How do I know if I'm eligible for Mounjaro in the UK?
You're generally eligible if you have a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions (type 2 diabetes, high blood pressure, sleep apnoea, cardiovascular disease). South Asian, Chinese, Black African, and Black Caribbean adults may be eligible at lower BMI thresholds. A licensed prescriber assesses your individual suitability following a clinical assessment.
Is Mounjaro the same as Wegovy?
No. Both are prescription weight loss injections licensed in the UK, but Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, whilst Wegovy (semaglutide) is a GLP-1 agonist only. In clinical trials, Mounjaro showed slightly higher average weight loss (15–21% body weight) compared to Wegovy (approximately 15%), though individual results vary. Your prescriber will recommend the most appropriate option for you.
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.