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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Does Mounjaro cause neck pain compared to Wegovy?
Neck pain and stiffness are not commonly reported side effects of either Mounjaro or Wegovy in clinical trials. Both are GLP-1-based weight loss injections prescribed in the UK, though they work slightly differently. If you're experiencing neck discomfort whilst taking either medication, it's important to report this to your GP or prescriber, as it may be unrelated to the injection itself. This guide compares both medications to help you understand their differences and side effect profiles in the UK context.
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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.
How Mounjaro and Wegovy differ in mechanism and side effects
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways to help regulate appetite and blood sugar. Wegovy (semaglutide) activates only the GLP-1 pathway, making it a single-mechanism medication. In clinical trials — SURMOUNT for Mounjaro and STEP for Wegovy — the most commonly reported side effects were nausea, diarrhoea, vomiting, and constipation. Neck pain was not listed as a frequent side effect in either trial. Both medications are prescribed as once-weekly injections in the UK following a clinical assessment. The dual action of Mounjaro may result in slightly higher average weight loss (15–21% body weight) compared to Wegovy (approximately 15%), though individual results vary significantly.
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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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Which medication might be right for you — and how to decide
Whether Mounjaro or Wegovy is more suitable depends on your individual health, medical history, and how you respond to treatment. Your GP or a licensed prescriber will assess your BMI, existing health conditions, current medications, and any previous reactions to similar treatments. You can use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses, though this is not a substitute for medical advice. Neither medication is assured to work the same way for everyone. If you experience neck pain whilst on either medication, contact your prescriber promptly — they can assess whether it's related to the injection or another cause, and discuss alternatives 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.
Can Mounjaro cause neck stiffness or pain?
Neck pain is not a commonly reported side effect of Mounjaro in clinical trials. Very common side effects include nausea, diarrhoea, vomiting, and constipation. If you develop neck pain whilst taking Mounjaro, report it to your GP or prescriber — it may be unrelated to the medication or require dosage adjustment.
Is Wegovy safer for the neck than Mounjaro?
Both medications have similar side effect profiles regarding neck complaints. The most common side effects of Wegovy are gastrointestinal (nausea, diarrhoea, constipation). Neither medication lists neck pain as a frequent adverse effect. Individual responses vary, so what suits one person may not suit another.
What should I do if I get neck pain on weight loss injections?
Contact your GP or prescriber immediately. Neck pain could be unrelated to the medication, linked to posture changes during weight loss, or a sign to pause or adjust your dose. Never stop your medication without medical guidance — your prescriber can assess and advise.
How do I know which medication — Mounjaro or Wegovy — is right for me?
A UK-licensed prescriber will assess your BMI, health conditions, and medical history to recommend the most suitable medication. Both require a clinical assessment before prescription. Use our free GLP-1 calculator to compare projected outcomes, then discuss the results with your prescriber.
Are Mounjaro and Wegovy prescribed the same way on the NHS?
Both are available through NHS specialist tier 3 weight management services (with varying regional access and waiting times) or through private online prescribing following a clinical assessment. Availability and waiting lists differ significantly by area, so ask your GP about local options. ```
Ready to take control of your weight loss journey?
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