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 and Bone Density — What You Need to Know
Weight loss medications like Mounjaro (tirzepatide) can help reduce body weight, but emerging research suggests gradual weight management may affect bone density in some individuals. This guide explains what current evidence shows about Mounjaro and bone health, who may be at higher risk, and what monitoring your GP may recommend. Understanding this potential link is important for anyone considering this prescription-only injection as part of their weight management journey.
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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.
What Does Research Show About GLP-1 Medications and Bone Health?
Clinical research on GLP-1 and tirzepatide (Mounjaro) medications is still developing regarding bone density effects. Early data from GLP-1 weight loss studies suggests that gradual weight management itself—rather than the medication specifically—may contribute to some bone density reduction. This is because bone density is partly supported by body weight, and losing weight quickly can affect calcium metabolism and bone turnover.
A key consideration: any medication causing significant weight loss may have bone health implications. The degree of risk appears to relate to:
- Speed of weight loss (faster loss = greater potential impact)
- Baseline bone health before starting treatment
- Age and sex (post-menopausal women face higher osteoporosis risk generally)
- Dietary calcium and vitamin D intake
- Physical activity levels
Current evidence does not show that tirzepatide directly damages bone tissue, but the metabolic changes during gradual weight management warrant monitoring by your GP.
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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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What Your GP Should Monitor and How to Protect Bone Health
If you're prescribed Mounjaro, inform your GP about any family history of osteoporosis or previous bone fractures. Your doctor may recommend baseline bone health screening (DEXA scan) before starting, particularly if you're over 50, post-menopausal, or have other risk factors.
Protective measures include:
- Adequate calcium intake: Aim for 1,000–1,200 mg daily from dairy, leafy greens, or supplements
- Vitamin D: Especially important in the UK—discuss supplementation with your GP
- Weight-bearing exercise: Walking, strength training, and resistance work support bone strength
- Slower weight loss: NHS recommends 0.5–1 kg per week; faster loss increases metabolic stress on bones
- Regular monitoring: Your GP may recommend repeat DEXA scans or blood tests during treatment
Use our free BMI calculator to track your weight loss progress and ensure you're losing at a sustainable, healthy rate.
- 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 weaken bones?
Current evidence suggests Mounjaro (tirzepatide) does not directly damage bone tissue. However, gradual weight management from any cause—including GLP-1 medications—may affect bone density metabolism. This is why monitoring by your GP is important, particularly if you have risk factors for osteoporosis.
Who is most at risk of bone density issues on Mounjaro?
Higher-risk groups include post-menopausal women, adults over 50, those with a family history of osteoporosis, people with low baseline vitamin D or calcium intake, and individuals losing weight very rapidly. Your GP can assess your individual risk profile before prescribing.
What screening should I have before starting Mounjaro?
Your GP may recommend a baseline DEXA scan (bone density scan) before starting Mounjaro, especially if you have risk factors. Blood tests checking calcium, vitamin D, and bone turnover markers may also be done. Discuss your bone health history with your prescriber during your clinical assessment.
How can I protect my bones while on Mounjaro?
Ensure adequate calcium (1,000–1,200 mg daily) and vitamin D intake, engage in regular weight-bearing exercise, maintain a healthy weight loss rate (0.5–1 kg per week), and attend follow-up appointments with your GP. These measures support bone health during weight loss treatment.
Should I avoid Mounjaro if I have osteoporosis risk?
Not necessarily. Having osteoporosis risk doesn't automatically exclude you from Mounjaro, but it means your GP will want to monitor you more closely. Prescription weight loss may still be beneficial if your health risks from excess weight outweigh bone health concerns. Your prescriber will discuss this with you during your clinical assessment.
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