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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Mounjaro Back Ache — Causes, Cost & UK Access
Back ache is not listed as a common side effect of Mounjaro (tirzepatide), though some users report muscle or joint discomfort. If you experience back pain while taking Mounjaro, it's important to discuss this with your GP or prescriber. This guide explains what we know about Mounjaro and musculoskeletal symptoms, how to access Mounjaro in the UK, and the real costs involved whether you choose NHS or private prescription routes.
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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.
Understanding Mounjaro Back Pain and UK Prescription Costs
Back ache is not formally reported in Mounjaro clinical trials as a common or very common side effect. However, some patients describe muscle aches, joint pain, or general body discomfort during treatment. This may be related to gradual weight management itself — losing weight quickly can temporarily strain joints and muscles, especially around the spine and lower back. Weight loss of 15–21% over several months, as seen in clinical trials, represents significant change for your musculoskeletal system.
If you experience back pain on Mounjaro:
- Inform your GP or prescriber — they can assess whether it's related to the medication, the weight loss process, or another cause
- Maintain gentle physical activity and stretching where comfortable
- Ensure adequate hydration and nutrition during weight loss
- Consider physiotherapy or osteopathy for support
Mounjaro is available through NHS specialist weight management services or private prescription. NHS access typically involves referral to a tier 3 weight management service, though regional availability varies significantly. Private prescriptions range from £150–£320 per month depending on your dose and provider, with costs highest at the maximum 15 mg dose.
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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.
NHS vs Private Mounjaro Access in the UK
NHS route: Your GP refers you to a specialist weight management service (tier 3 or 4) if you meet eligibility criteria — typically BMI 30+ or 27+ with weight-related health conditions. Assessment and prescribing happen through the specialist service. Waiting times vary by region (NHS ICB) and can be several months to over a year in some areas. Once approved, Mounjaro is dispensed through NHS pharmacies at standard prescription cost (£11.90 in England, or free if you qualify for exemption).
Private route: Online consultation with a UK-licensed prescriber — no GP referral needed. If approved, your prescription goes to a GPhC-registered pharmacy. Results typically within 24–48 hours. Costs £150–£320/month depending on tirzepatide dose. No NHS waiting list, but you bear the full cost. Use our free GLP-1 weight loss calculator to explore potential outcomes before deciding.
You can also use our free BMI calculator above to check your current BMI and understand your eligibility context. Both NHS and private routes require a clinical assessment confirming you meet eligibility criteria and that Mounjaro is appropriate for your health profile. Your prescriber will review your medical history, current medications (particularly oral contraceptives — Mounjaro can reduce their effectiveness), and any previous GI conditions. Ask your prescriber about realistic timeframes for dose titration, potential side effects, and when to expect weight loss to begin.
- 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 ache is not listed as a common or very common side effect in Mounjaro clinical trials. However, some patients report muscle or joint discomfort, which may relate to gradual weight management straining the musculoskeletal system rather than the medication directly. Always report any new or persistent back pain to your prescriber.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs range from approximately £150–£320 per month depending on your tirzepatide dose (2.5 mg to 15 mg). The KwikPen contains 4 weeks of injections. Some private providers offer payment plans or subscription discounts. Prices vary between registered pharmacies, so compare before committing.
Can I get Mounjaro free on the NHS in the UK?
Yes, if you're referred to an NHS specialist weight management service and approved, Mounjaro is dispensed through NHS pharmacies at standard prescription cost (£11.90 in England, free if exempt). However, NHS access varies significantly by region, and waiting times can be very long. Ask your GP about your local tier 3 weight management service availability.
What's the difference between the NHS and private route for Mounjaro?
NHS requires GP referral to specialist services, clinical assessment, and potential waiting lists, but costs only £11.90 per prescription once approved. Private prescribing is faster (24–48 hours), needs no GP referral, but costs £150–£320/month. Both require a UK prescriber's assessment and confirmation you meet eligibility criteria.
What dose of Mounjaro would I start on?
Mounjaro dose titration begins at 2.5 mg weekly, increasing every 4 weeks by 2.5 mg increments (5 mg, 7.5 mg, 10 mg, 12.5 mg) up to a maximum of 15 mg. Your prescriber adjusts the pace based on tolerability and response. Most people find their effective dose between 10–15 mg, though some see good results at lower doses.
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.