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
Does Mounjaro Injection Hurt?
Most people find Mounjaro injections cause minimal discomfort. The needle is very small, and most patients report only a slight sting or no pain at all. Some experience mild bruising or redness at the injection site, but severe pain is uncommon. Your experience may vary depending on needle sensitivity, injection technique, and skin thickness. If you're considering this prescription weight loss injection through NHS specialist services or private prescribing in the UK, understanding what to expect can help you feel more confident about the weekly injections.
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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 to Expect From Mounjaro Injections
Mounjaro is administered via a pre-filled KwikPen, a small, user-friendly injection device containing a very fine needle. The needle is only 4mm long and 31 gauge — thinner than most blood test needles. Most patients describe the sensation as a brief pinprick rather than genuine pain.
- Injection site reactions — redness, bruising, or minor swelling are common but usually resolve within hours
- Mild sting — most people feel a brief sharp sensation lasting less than a second
- No pain during the week — once injected, the medicine causes no ongoing discomfort
- Rotating injection sites — alternating between stomach, thigh, and upper arm helps minimise site irritation over time
If you're nervous about injections, your prescriber can discuss techniques to make the experience more comfortable, and many people find it becomes easier with practice.
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.
NHS Eligibility and What Your GP Should Know
In the UK, Mounjaro is available through NHS specialist tier 3 weight management services or via private prescription following a clinical assessment. Adults with a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions, may be eligible for this weekly weight loss injection.
NHS access varies by region — waiting lists can be lengthy in some areas. Your GP can refer you to your local specialist service, where a clinical team will assess whether Mounjaro is suitable for you. Private online prescribers can also assess eligibility if you prefer faster access. Either route requires a prescription and ongoing monitoring. Use our free GLP-1 weight loss calculator to explore potential outcomes, and our BMI calculator to check where you currently fall on NHS eligibility thresholds.
- 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 the Mounjaro needle painful?
No, most people experience only a brief pinprick sensation. The needle is very fine (31 gauge, 4mm long) and the injection takes less than a second. Pain is uncommon; mild stinging is more typical.
How often does injection site pain occur?
Injection site reactions (redness, bruising, mild swelling) affect fewer than 1 in 10 people. These are usually mild and resolve within hours. Rotating injection sites week to week reduces the risk.
Can I inject Mounjaro myself?
Yes, the KwikPen is designed for self-injection at home. Your prescriber or clinic nurse will show you the correct technique. Many people find self-injecting becomes comfortable after the first or second dose.
What if I'm needle-phobic?
Tell your prescriber or GP about needle anxiety. They can discuss techniques to make injections easier, such as applying numbing cream beforehand or having someone present for support.
Does the injection hurt more as you increase doses?
No, pain is not dose-related with Mounjaro. The needle size and injection technique remain the same at all doses (2.5mg to 15mg). You may experience more nausea at higher doses, but not injection pain.
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.