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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How Do I Know If I Injected Mounjaro Correctly?
When you're self-injecting Mounjaro (tirzepatide), it's natural to wonder if you've done it correctly. The good news is that most self-injections with the Mounjaro KwikPen are successful if you follow the prescribed technique. This guide explains what proper injection technique looks like, what to expect during and after injection, and when to contact your GP if you have concerns about your injection method.
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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.
Signs Your Mounjaro Injection Was Done Correctly
A correctly administered Mounjaro injection should feel like a quick, sharp pinch that lasts just one or two seconds. Here are the key signs that suggest your injection went well:
- The pen made a clicking sound — This audible or tactile click indicates the needle has been triggered and the medication is being delivered into the subcutaneous tissue (under the skin).
- You felt minimal pain — A tiny pinch is normal; severe pain suggests the needle may not be in the right place. Nerves are rare in subcutaneous tissue, so correct injections cause only mild discomfort.
- No blood appeared — A small amount of blood or clear fluid at the injection site is normal, but if you hit a blood vessel, you might see more bleeding. This is not dangerous but suggests the angle or location wasn't ideal.
- You could remove the pen smoothly — The pen should come away easily after the 3-second count. If it was difficult to remove or felt stuck, you may have tensed the skin excessively.
- No medication leakage — If liquid dripped or ran down your skin immediately after injection, some medication may not have entered the tissue. Pressing gently for a few seconds after removal helps prevent this.
Compare your experience with our GLP-1 weight loss calculator, which can help you track your doses and understand the expected timeline for each injection.
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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.
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Everything you need to understand your weight, explore medication options, and track your progress — completely free.
What to Do If You're Unsure About Your Injection
If you're uncertain whether your injection was delivered correctly, contact your GP or the prescribing service that issued your Mounjaro prescription. They can:
- Review your injection technique over the phone or video call
- Watch a video of you performing the injection if needed
- Arrange a face-to-face demonstration if you're having consistent problems
- Check whether any symptoms suggest the dose wasn't fully delivered
Do not skip your next dose or attempt to inject twice to make up for a missed or uncertain injection. If you believe an injection failed completely, wait until your next scheduled dose day and inform your prescriber at your next review. Taking Mounjaro as prescribed, even with minor imperfections in technique, is safer than trying to correct it yourself. Your prescriber can adjust your treatment plan if needed.
- 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.
What does it feel like when Mounjaro is injected correctly?
A correct Mounjaro injection feels like a quick, sharp pinch lasting one to two seconds. You should hear or feel a click from the KwikPen when the needle triggers. Minimal pain is normal; severe pain suggests incorrect technique. A small amount of clear fluid or blood at the site is also normal.
Is it bad if blood came out of my Mounjaro injection site?
A small amount of blood is not concerning and doesn't mean the injection failed. It simply means you may have grazed a small blood vessel just under the skin. This is harmless and does not affect the medication's delivery. If significant bleeding occurs, apply gentle pressure for a few seconds and inform your prescriber.
How do I know if my Mounjaro dose didn't go in?
Signs include medication visibly dripping or leaking down your skin immediately after injection, difficulty removing the pen, or unusually severe pain. However, most leakage is minimal and the dose still enters the tissue. If you're genuinely concerned, contact your prescriber. Do not attempt a second injection without their guidance.
What should I do if I think I did the injection wrong?
Contact your GP or the prescribing service that issued your Mounjaro UK prescription. They can review your technique and provide guidance. Do not skip your next dose or inject twice. Your prescriber will advise whether any action is needed based on your specific situation.
Can a poorly injected Mounjaro still work?
Even if your technique wasn't perfect, most Mounjaro injections still deliver the medication effectively into the subcutaneous tissue. Minor variations in technique rarely prevent the dose from working. If you have ongoing concerns or notice no weight loss after several doses, discuss this with your prescriber rather than assuming the injection failed.
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.