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
Free tracker included with every download this week
Does Mounjaro Lower Testosterone?
There is no clinical evidence that Mounjaro (tirzepatide) directly lowers testosterone levels. Testosterone changes are not listed as a side effect in the UK product information or the SURMOUNT clinical trials. However, testosterone can be indirectly affected by gradual weight management itself, which may occur during Mounjaro treatment. If you have concerns about hormone levels whilst taking this prescription medication, your GP can arrange blood tests to monitor your health during treatment.
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Calculate Your BMI Instantly
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 the Clinical Evidence Show?
Mounjaro is not known to lower testosterone directly. The SURMOUNT trials, which tested tirzepatide in thousands of adults, did not report testosterone changes as a side effect. Testosterone is also not listed in the UK product information for Mounjaro as an expected hormonal effect of the medication.
However, weight loss itself can affect hormone levels, including testosterone. When significant weight loss occurs — particularly gradual weight management — some individuals may experience temporary changes in testosterone production. This is not caused by the Mounjaro dose titration process itself, but by the metabolic changes associated with losing excess weight. This effect is typically temporary and often reverses as weight stabilises.
- Mounjaro is a dual GIP and GLP-1 receptor agonist that works on appetite regulation, not directly on hormone production
- The medication slows gastric emptying and reduces food cravings, supporting calorie deficit
- Hormone monitoring can be arranged by your GP if you have specific concerns
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
When Should You Discuss Hormone Health with Your GP?
If you have a personal or family history of hormone-related conditions, or if you notice symptoms like fatigue, mood changes, or reduced libido whilst taking Mounjaro, speak to your GP. They can arrange blood tests to check your testosterone levels and other hormones if clinically appropriate. Weight loss itself can affect hormone levels, so baseline testing before starting treatment and follow-up testing during weight loss can help distinguish between medication effects and weight loss-related changes.
Your GP can also assess whether Mounjaro eligibility fits your individual health profile. Our GLP-1 weight loss calculator can help you understand potential weight loss trajectories, which may help you discuss realistic timelines with your healthcare provider.
- 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 tirzepatide affect testosterone production?
No — tirzepatide (Mounjaro) does not directly target or reduce testosterone production. Clinical trials did not identify testosterone changes as a side effect. However, gradual weight management from any cause can temporarily affect hormone levels in some individuals.
Is testosterone loss a known side effect of Mounjaro in the UK?
No. The UK product information for Mounjaro does not list testosterone changes as a side effect. Testosterone is not monitored routinely in clinical trials of this medication, as direct hormonal effects were not identified.
Can weight loss from Mounjaro affect my testosterone?
Potentially, yes — but indirectly. Rapid or significant weight loss can temporarily affect testosterone and other hormone levels in some people. This is not specific to Mounjaro; it can happen with any substantial weight loss. The effect is often temporary.
Should I have my testosterone checked before starting Mounjaro?
If you have specific concerns about hormone health, your GP can arrange baseline blood tests before starting treatment. This helps establish your baseline and allows for monitoring if you notice symptoms during weight loss. Mounjaro is prescription-only and requires clinical assessment first.
What should I do if I notice hormone-related symptoms on Mounjaro?
Contact your GP if you experience persistent fatigue, mood changes, or other hormone-related symptoms. They can review your symptoms, check your testosterone and other hormone levels if appropriate, and assess whether Mounjaro remains suitable for you or whether adjustments are needed.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.