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 Affect Bone Density?
Mounjaro (tirzepatide) is a prescription-only weight management injection that has become increasingly available in the UK through NHS specialist services and private prescribing. As with any medication affecting weight loss, questions about bone health are important. Current evidence suggests that weight loss itself, rather than Mounjaro specifically, may influence bone density. This guide explains what research shows about tirzepatide, bone health, and what you should discuss with your GP if you're considering this treatment.
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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.
What the Research Shows About Weight Loss and Bone Density
Bone density changes during weight loss are a recognised area of medical interest. When people lose weight, including through medications like Mounjaro or other GLP-1 receptor agonists, bone mineral density may decrease slightly in some individuals. This is because bone adapts to reduced mechanical load as body weight decreases.
However, the clinical significance of modest bone density reductions during weight loss remains unclear. Research from weight loss studies shows that while some decrease in bone density can occur, fracture risk does not necessarily increase proportionally. The SURMOUNT clinical trials for tirzepatide did not identify bone density or fracture risk as a primary safety concern, though longer-term data continues to be collected.
- Weight loss itself, not the medication, is the main factor affecting bone density
- Bone density changes are often modest and may stabilise over time
- Maintaining physical activity and adequate calcium intake helps protect bone health during weight loss
- Individual factors like age, sex, and baseline bone health influence response
Your GP can assess your individual bone health risk, particularly if you have risk factors for osteoporosis.
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If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
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Protecting Bone Health While Taking Mounjaro
If you're prescribed Mounjaro through an NHS specialist weight management service or a private prescriber, protecting your bone health is straightforward. Maintain regular physical activity, including weight-bearing exercise like walking or strength training, which supports bone density. Ensure adequate calcium intake through diet (dairy, leafy greens, fortified foods) or discuss supplements with your GP if needed. Vitamin D is equally important for bone health — UK adults should aim for 10 micrograms daily, and supplementation is often recommended in winter months.
Your prescriber or GP should discuss bone health as part of your overall assessment, particularly if you have a family history of osteoporosis, are post-menopausal, or have other risk factors. Use our GLP-1 weight loss calculator to understand projected weight loss, then discuss bone health implications with your healthcare provider during your clinical assessment.
If you're prescribed Mounjaro through an NHS specialist weight management service or a private prescriber, protecting your bone health is straightforward. Maintain regular physical activity, including weight-bearing exercise like walking or strength training, which supports bone density. Ensure adequate calcium intake through diet (dairy, leafy greens, fortified foods) or discuss supplements with your GP if needed. Vitamin D is equally important for bone health — UK adults should aim for 10 micrograms daily, and supplementation is often recommended in winter months.
Your prescriber or GP should discuss bone health as part of your overall assessment, particularly if you have a family history of osteoporosis, are post-menopausal, or have other risk factors. Use our GLP-1 weight loss calculator to understand projected weight loss, then discuss bone health implications with your healthcare provider during your clinical assessment.
- 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.
Does Mounjaro directly damage bone density?
No. Current evidence suggests that weight loss itself, rather than tirzepatide specifically, may influence bone density. The SURMOUNT clinical trials did not identify bone density as a primary safety concern with Mounjaro. Individual bone health depends on multiple factors including age, physical activity, and nutrition.
Should I worry about fractures if I take Mounjaro?
Fracture risk is not listed as a common concern in Mounjaro safety data. However, if you have risk factors for osteoporosis (family history, post-menopause, long-term steroid use), discuss bone health with your GP before starting treatment. They can assess your individual risk.
What can I do to protect my bones while losing weight?
Weight-bearing exercise (walking, strength training) helps protect bone density. Ensure adequate calcium (1,000mg daily for adults) and vitamin D (10 micrograms daily). Your GP can assess whether supplements are needed based on your individual circumstances.
Will my bone density recover after stopping Mounjaro?
Bone density often stabilises or improves with continued weight maintenance and good nutrition. If you stop Mounjaro, bone health depends on maintaining healthy weight, exercise, and calcium/vitamin D intake. Discuss long-term management with your GP.
Should I have a bone density scan before starting Mounjaro?
This depends on your age, sex, and individual risk factors. Your GP or prescriber will assess whether a baseline scan is needed. DEXA scans are not routinely required before starting weight loss treatment unless you have specific osteoporosis risk factors.
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