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
Can Mounjaro Cause Back Pain?
Back pain is not listed as a common side effect of Mounjaro (tirzepatide) in UK clinical trials or prescribing information. However, weight-related conditions can cause back pain, and gradual weight management may temporarily affect posture and muscle support. If you experience new or worsening back pain while taking Mounjaro, it's important to discuss this with your GP. They can assess whether the pain is related to your medication, underlying health conditions, or changes in your body composition as you lose weight. Always inform your prescriber of any new symptoms during treatment.
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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.
How Weight Loss Affects the Back
Back pain and excess weight are closely connected. Carrying extra weight places additional stress on your spine, lower back muscles, and joints — particularly if weight is concentrated around the abdomen. This is why people with a higher BMI often experience increased back pain. When you lose weight, this pressure reduces, which may actually improve back pain for many people.
However, gradual weight management can sometimes cause temporary discomfort as your body adjusts. Your muscles, ligaments, and posture may shift as you lose weight, particularly if you're not maintaining muscle strength through physical activity. This is different from a medication side effect — it's a natural consequence of significant body composition change. Our free BMI calculator can help you track how weight changes relate to your health profile.
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
When to Contact Your GP About Back Pain
If you develop back pain while taking Mounjaro, contact your GP if the pain is:
- Severe or persistent (lasting more than two weeks)
- Accompanied by numbness, tingling, or weakness in your legs
- Affecting your ability to move or carry out daily activities
- Spreading from your back to other areas
- Not improving with rest or paracetamol
Your GP can examine you, rule out other causes, and advise whether to continue Mounjaro. They may also recommend physiotherapy or lifestyle adjustments to support your back as you lose weight. Use our GLP-1 weight loss calculator to understand your projected weight changes, which can help you and your GP discuss realistic timelines.
- 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 back pain a known side effect of Mounjaro?
Back pain is not listed as a common side effect of Mounjaro in UK clinical trials or the prescribing information. Very common side effects include nausea, diarrhoea, constipation, and stomach pain. If you experience back pain while taking Mounjaro, discuss it with your GP to rule out other causes or underlying health conditions.
Can losing weight with Mounjaro help my existing back pain?
For many people, losing weight reduces pressure on the spine and lower back, which may improve chronic back pain. However, gradual weight management can temporarily cause muscle soreness or postural adjustments. Combining weight loss with physiotherapy and regular, gentle exercise helps protect your back during the weight loss process.
Should I stop taking Mounjaro if I develop back pain?
Do not stop taking Mounjaro without medical advice. Contact your GP to discuss your symptoms. They can assess whether the pain is related to your medication, your weight loss, or another condition. Your prescriber may adjust your dose or recommend additional support while you continue treatment.
What's the difference between Mounjaro and Wegovy for back pain risk?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) may cause similar common side effects, but back pain is not listed for either medication. Both are prescription-only and require clinical assessment. Your GP can discuss which option may be most suitable for your individual health profile.
Can gradual weight management from Mounjaro cause back problems?
gradual weight management can temporarily affect posture and muscle strength, potentially causing back discomfort. However, this is not a side effect of the medication itself — it's a natural adjustment. Maintaining physical activity, good posture, and core strength during weight loss helps protect your back. Aim for sustainable loss of 0.5–1 kg per week, which is the NHS-recommended rate.
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.