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
Back Pain On Mounjaro — How Does It Compare To Wegovy?
Back pain is not listed as a common side effect of either Mounjaro (tirzepatide) or Wegovy (semaglutide) in UK clinical trials. However, both GLP-1 medications can cause musculoskeletal changes related to gradual weight management, dehydration, or muscle loss — which may indirectly lead to pain. This guide explains the key differences between Mounjaro and Wegovy, their mechanisms, and how your GP or prescriber can help assess which prescription injection might be more suitable for you alongside lifestyle changes.
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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.
Clinical Trial Data And Mechanism Differences
Back pain is not formally reported as a frequent side effect in the SURMOUNT clinical trial (Mounjaro) or the STEP trials (Wegovy). However, both medications work through similar hormonal pathways that can affect the body during weight loss. Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy is a GLP-1 receptor agonist only — this dual mechanism may mean Mounjaro produces slightly different metabolic effects. In trials, Mounjaro showed average weight loss of approximately 15–21% body weight, whilst Wegovy achieved around 14.9% on average. gradual weight management can sometimes cause muscle strain, dehydration, or electrolyte changes that may trigger musculoskeletal discomfort. Your GP or prescriber can assess your full medical history to determine suitability.
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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.
Individual Suitability And Prescriber Assessment
Neither Mounjaro nor Wegovy is automatically "better" for back pain — suitability depends entirely on your individual health profile, existing conditions, and medications. If you have a history of back problems, inform your prescriber before starting any GLP-1 medication. Both tirzepatide (Mounjaro) and semaglutide (Wegovy) require a UK prescription and clinical assessment. Your GP or a licensed prescriber will evaluate your BMI, weight-related health conditions, and medical history to determine which option is appropriate. Staying hydrated, maintaining adequate protein intake, and combining medication with gentle exercise can help support musculoskeletal health during weight loss.
- 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 or Wegovy?
Back pain is not listed as a common or very common side effect in the SURMOUNT (Mounjaro) or STEP (Wegovy) clinical trials. However, gradual weight management, muscle loss, dehydration, or postural changes during treatment can indirectly cause musculoskeletal discomfort. Always report any new pain to your GP.
How do Mounjaro and Wegovy differ in their mechanism?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, whilst Wegovy (semaglutide) is a GLP-1 receptor agonist only. This means Mounjaro activates two hormone pathways, which may produce different metabolic and appetite-suppressing effects. Individual responses vary.
Which injection causes more musculoskeletal side effects?
Neither Mounjaro nor Wegovy has a higher rate of musculoskeletal pain in clinical trials. Side effect profiles are broadly similar between the two. Any musculoskeletal issues should be discussed with your prescriber, who can advise whether to continue treatment.
Can I use the weight loss calculator to compare Mounjaro vs Wegovy outcomes?
Yes — use our free GLP-1 weight loss calculator above to see projected outcomes at different doses for both medications. Results are estimates based on clinical trial averages; individual results vary significantly and depend on lifestyle changes.
How do I get Mounjaro or Wegovy prescribed in the UK?
Both are prescription-only medicines available through NHS specialist tier 3 weight management services or private online prescribing. Your GP can refer you to NHS services, or you can seek a private clinical assessment with a UK-licensed prescriber. Eligibility requires a BMI of 30+ or 27+ with weight-related health conditions.
Ready to take control of your weight loss journey?
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