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, Bone Density, and How It Compares to Wegovy
Both Mounjaro and Wegovy are prescription-only weight loss injections used in the UK, but bone density changes during weight loss are an important health consideration. This guide compares what clinical evidence shows about these medications, how they work differently, and what you should discuss with your GP or prescriber. Weight loss itself can affect bone density, so understanding the full picture matters when choosing a treatment approach.
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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 Evidence and Mechanism Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist approved for weight management in UK adults. Clinical trials showed average weight loss of 15–21% body weight depending on dose, though individual results vary. Wegovy (semaglutide) is a single GLP-1 receptor agonist with average weight loss around 14–15% in trials.
Regarding bone density specifically, neither medication has bone loss as a primary focus in clinical trials. However, gradual weight management from any source—including medication—can trigger bone remodelling and temporary decreases in bone mineral density. The SURMOUNT-1 trial (Mounjaro) and STEP-1 trial (Wegovy) measured metabolic markers but bone density changes were not a primary outcome. Your prescriber can discuss individual bone health risk factors based on your age, sex, and medical history when assessing suitability for either tirzepatide.
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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.
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Individual Suitability and Prescriber Assessment
Both Mounjaro and Wegovy require a clinical assessment before prescription. Your GP or UK-licensed prescriber will review your full medical history, including bone health risk factors such as age, family history, calcium intake, and previous bone density screening. Use our free BMI calculator above to check your starting point, then discuss with your prescriber whether either medication is appropriate for you.
Weight loss itself—whether achieved through diet, exercise, or medication—can affect bone density, so sustained adequate nutrition, calcium, vitamin D, and physical activity are important throughout any weight loss journey. Your prescriber may recommend bone health monitoring if you have risk factors for osteoporosis.
Neither Mounjaro nor Wegovy has specific bone density concerns that would make one clearly superior to the other for bone health. The choice between them depends on individual factors including your BMI, weight-related health conditions, other medications, side effect profile, and prescriber recommendation. Access in the UK is through NHS specialist weight management services (with potentially long waiting lists in many areas) or private online prescribing following clinical assessment. Try our free GLP-1 weight loss calculator to explore projected outcomes at different doses, then discuss your options with your prescriber.
- 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.
Can Mounjaro or Wegovy cause bone loss?
Both medications can cause weight loss, which may trigger temporary bone remodelling and decrease bone mineral density—but this is a general effect of weight loss, not specific to these medications. Adequate calcium, vitamin D, and weight-bearing exercise help protect bone health during weight loss. Your GP can assess individual bone health risk factors.
Which is better for bone health, Mounjaro or Wegovy?
Clinical trials for both medications did not focus on bone density as a primary outcome. Neither has clear bone health advantages over the other. Bone health during weight loss depends more on individual factors like age, nutrition, and exercise than on the choice of medication. Your prescriber can advise based on your personal risk profile.
How much weight loss affects bone density?
Bone density changes depend on the rate of weight loss, individual metabolism, nutritional status, and exercise. Gradual weight loss (0.5–1 kg per week, as the NHS recommends) with adequate nutrition and physical activity generally has less impact on bone health than gradual weight management. Discuss your weight loss plan with your GP.
Do I need bone density screening before starting Mounjaro or Wegovy?
Not routinely—but your prescriber will assess your individual risk factors for bone health problems. You may need screening if you're over 50, have a family history of osteoporosis, low body weight, or take certain medications. Discuss bone health screening with your GP during your clinical assessment.
How do I protect bone health while taking a weight loss injection?
Ensure adequate calcium (1,000–1,200 mg daily) and vitamin D, do regular weight-bearing exercise, avoid smoking, and limit alcohol. Your GP or prescriber can advise on supplementation if needed. Track your progress with our free progress tracker and discuss any concerns about bone health at your regular health reviews.
Ready to take control of your weight loss journey?
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