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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Mounjaro First Dose: What to Expect and How to Access It in the UK
Starting Mounjaro (tirzepatide) can feel like a big step. Your first dose is typically 2.5 mg—a low starting point designed to help your body adjust before gradual increases over weeks. Whether you're accessing Mounjaro through the NHS or private prescription in the UK, understanding what happens at your first injection and what costs to expect will help you feel confident and prepared for your weight management journey.
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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.
What Happens at Your First Mounjaro Dose
Your first Mounjaro injection is 2.5 mg, delivered once weekly using a pre-filled KwikPen device. This dose is intentionally low—it's an adjustment phase, not the therapeutic dose. You'll inject into your stomach, thigh, or upper arm (though the arm requires assistance), and most people experience minimal injection site discomfort.
- Injection takes about 5 seconds
- The needle is very fine (29 gauge)
- Many people feel nothing during the injection
- Some experience mild redness or bruising at the site—this is normal
You'll stay on 2.5 mg for 4 weeks before your prescriber reviews how you've tolerated it. Common early effects include nausea (usually mild), reduced appetite, and possible mild digestive changes. These typically ease within the first 1–2 weeks. Use our free GLP-1 weight loss calculator to see how weight loss projections may change as your dose increases over the following weeks and months.
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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.
UK Prescription Access: NHS vs Private Route and Costs
NHS access: Mounjaro is available through NICE-approved NHS specialist weight management services (tier 3/4). You'll need a GP referral, and waiting times vary significantly by region—some areas have waits of several months. Once approved, Mounjaro is provided free on prescription.
Private access: You can access Mounjaro privately through an online consultation with a UK-licensed prescriber, without needing an NHS referral. This is faster—typically within days. Private costs range from approximately £129–£180 per month depending on your dose. A basic online consultation fee (£20–£50) is usually charged separately. Private prescriptions are dispensed by GPhC-registered pharmacies. Use our free BMI calculator to confirm your eligibility before pursuing either route.
What the online consultation involves: You'll answer questions about your medical history, weight, height, current medications, and weight loss goals. The prescriber reviews this information and decides if tirzepatide is suitable for you. If approved, your prescription is sent electronically to a pharmacy, which dispatches your Mounjaro KwikPen within 1–2 working days. Before your first injection, you should receive guidance on injection technique—either via video tutorial or phone support. Always inform your prescriber if you're taking oral contraceptives (you'll need additional contraception for 4 weeks) or other regular medications, as Mounjaro can affect their absorption.
- 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.
Does the NHS cover Mounjaro for weight loss?
Yes, NICE has approved tirzepatide for NHS specialist weight management services. Access is through tier 3/4 specialist services via GP referral. Availability and waiting times vary significantly by region and ICB. Once prescribed through the NHS, Mounjaro is free on prescription, though waits can be several months in many areas.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs approximately £129–£180 per month depending on your dose (2.5 mg to 15 mg). An online consultation fee (£20–£50) is typically charged separately. Costs vary slightly between providers. Always check with the pharmacy for the exact price of your specific dose before committing.
Will I feel the Mounjaro injection?
Most people feel very little or nothing during the injection. The needle is very fine (29 gauge), and the injection takes about 5 seconds. Some experience mild pressure rather than pain. Mild redness or bruising at the injection site is normal and typically resolves within hours or days.
What dose do I start on and when do I increase?
You start on 2.5 mg—a low adjustment dose. You stay on this for 4 weeks, then your prescriber may increase to 5 mg if tolerated well. After that, doses typically increase every 4 weeks (to 7.5 mg, 10 mg, 12.5 mg, and finally 15 mg) based on your response and side effects. Never increase doses without guidance from your prescriber.
How quickly can I start Mounjaro privately?
Private access is typically much faster than NHS. You can usually have an online consultation within days, and if approved, your Mounjaro KwikPen is dispatched within 1–2 working days. NHS access can take several months depending on referral waiting lists and regional availability.
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.