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
If you're considering Mounjaro (tirzepatide) for weight management, you may have questions about how it affects bone health. Weight loss itself can influence bone density, and it's important to understand what this means for you and how your GP will monitor your health. This guide explains the evidence, what changes to expect, and how to support your bone health during weight loss treatment in the UK.
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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.
How Weight Loss Affects Bone Density
Bone density naturally decreases during weight loss because bone has less weight to support. Research shows that rapid or significant weight loss—particularly more than 1–2 kg per week—carries a higher risk of bone density loss compared to slower, sustainable weight loss.
Mounjaro and bone health: Clinical trials for Mounjaro (tirzepatide) did not identify bone density loss as a common side effect at standard doses. However, the medication does support significant weight loss—on average 15–21% of body weight in clinical trials—which means bone density changes are theoretically possible, particularly over longer periods.
- Slower weight loss (0.5–1 kg per week) minimises bone density risk
- Supporting bone health during weight loss is important and preventable
- Your GP can arrange bone density screening if appropriate for your age and health
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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.
Monitoring and Protecting Bone Health
When prescribed Mounjaro through NHS specialist services or a private prescriber, your initial health assessment will consider your risk factors for bone health changes. This includes your age, sex, family history, and any previous bone conditions.
How to support your bones during weight loss: Adequate calcium intake (1,000–1,200 mg daily), vitamin D (especially important in the UK), weight-bearing exercise, and avoiding gradual weight management all help protect bone density. If you're over 50 or have risk factors for osteoporosis, discuss bone health monitoring with your GP before starting Mounjaro or any weight loss treatment.
- 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 bones?
No. Mounjaro itself is not reported to directly harm bone tissue. The concern is that gradual weight management—which Mounjaro supports—can lead to temporary bone density changes because bone has less mechanical load to carry. This risk is minimised with slower, sustainable weight loss alongside adequate nutrition.
How quickly will my bones be affected by weight loss?
Bone density changes typically appear after several months of significant weight loss. The risk is much lower with gradual weight loss (0.5–1 kg per week) compared to rapid loss. Staying within NHS weight loss guidance significantly reduces bone health risk during Mounjaro treatment.
What can I do to protect my bones while taking Mounjaro?
Eat adequate calcium (dairy, leafy greens, fortified foods), take vitamin D (especially important in the UK's climate), do weight-bearing exercise like walking or resistance training, and avoid very gradual weight management. Discuss any bone health concerns with your GP before starting treatment.
Will my GP check my bone density if I take Mounjaro?
Not routinely for all patients—screening is typically offered if you have risk factors (age over 50, family history of osteoporosis, previous fractures, or certain medical conditions). Your prescriber will assess your individual risk during the initial consultation.
Is Mounjaro safe for my bones compared to Wegovy?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) carry the same theoretical bone density risk because it relates to weight loss itself, not the specific medication. Clinical data shows both are safe at standard doses when weight loss is gradual and nutrition is adequate. Your GP or prescriber can advise which is appropriate for you.
Ready to take control of your weight loss journey?
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