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 vs Wegovy: Hair Loss and Side Effects Compared
Hair loss is a reported side effect of both Mounjaro and Wegovy, though it affects only a minority of users. Both are prescription-only weight loss injections used in the UK, but they work differently—Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy is a GLP-1 agonist only. Understanding the differences in mechanism, clinical trial data, and potential side effects can help you and your prescriber make an informed decision about which weekly weight loss injection might be suitable for you following a clinical assessment.
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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.
Clinical Trial Data: Hair Loss Frequency and Mechanisms
Hair loss (alopecia) was reported in clinical trials for both medications, though it remains a less common side effect. In the SURMOUNT-1 trial for Mounjaro (tirzepatide), hair loss was reported as a common side effect occurring in up to 1 in 10 people. In the STEP-1 trial for Wegovy (semaglutide), hair loss was also documented but typically reported less frequently than with Mounjaro. Both medications work on appetite regulation pathways that may indirectly affect hair growth cycles, particularly during periods of gradual weight management when nutrient allocation shifts. The reason hair loss occurs is not fully understood but is thought to relate to the metabolic stress of weight loss itself rather than the medication directly targeting hair follicles. Important context: gradual weight management from any cause—whether through calorie restriction, medication, or surgery—can temporarily increase shedding. Hair typically regrows once weight stabilises and nutrient intake is adequate. Individual experience varies significantly; many users report no hair loss at all.
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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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Key Differences: GLP-1 vs Dual GIP+GLP-1 and Individual Suitability
Wegovy (semaglutide) activates the GLP-1 hormone pathway only, whilst Mounjaro (tirzepatide) activates both GIP and GLP-1 pathways simultaneously. This dual mechanism may explain slightly different side effect profiles, though robust head-to-head trial data comparing hair loss directly between the two is limited. Clinical trials for Mounjaro showed average weight loss of approximately 15–21% of body weight, whilst Wegovy showed approximately 15% in comparable studies—both alongside reduced-calorie diet and increased physical activity. Neither medication is "better" for hair loss; suitability depends on your individual health profile, other medical conditions, and how you tolerate each medication. A UK prescriber conducting a clinical assessment will consider your personal circumstances. Try our GLP-1 weight loss calculator to explore potential outcomes, and use our free BMI calculator to understand your current health context.
- 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 cause more hair loss than Wegovy?
Clinical trial data suggests Mounjaro may have a slightly higher reported frequency of hair loss (up to 10%) compared to Wegovy, but individual variation is significant and many users experience no hair loss at all. Both are associated with temporary shedding during gradual weight management. Direct comparative data is limited, and your prescriber can discuss individual risk based on your health profile.
Why do GLP-1 injections cause hair loss?
Hair loss with GLP-1 medications is thought to be linked to the metabolic stress of gradual weight management rather than the medication directly damaging hair follicles. When the body loses weight quickly, it redirects nutrients and may temporarily shift hair growth cycles. Hair typically regrows once weight stabilises and nutrition is adequate.
Is hair loss from Mounjaro or Wegovy permanent?
No. Hair loss associated with GLP-1 medications is typically temporary and occurs during active weight loss. Once weight stabilises and adequate nutrition is maintained, hair regrowth is normal. If hair loss persists after reaching a stable weight, discuss this with your GP or prescriber as it may indicate other factors.
How can I reduce the risk of hair loss on these injections?
Ensure adequate protein intake (especially important during weight loss), maintain micronutrient levels including iron, zinc, and B vitamins, stay hydrated, and lose weight at a sustainable pace. Your prescriber may recommend nutritional support or referral to a dietitian, particularly if significant hair loss occurs. Nutritional deficiency can worsen shedding.
Which is better—Mounjaro or Wegovy—for avoiding side effects?
Neither is universally "better"; both are prescription-only and require clinical assessment. Side effect tolerance is highly individual. Your GP or prescriber will assess whether Mounjaro's dual GIP+GLP-1 mechanism or Wegovy's GLP-1-only approach is more suitable for your health profile, medical history, and potential drug interactions. Both have strong clinical evidence.
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