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, Libido, and Sexual Function — What the Evidence Shows
Changes in libido and sexual function are not commonly reported side effects of Mounjaro (tirzepatide) in clinical trials, though individual experiences vary. This guide explains what the evidence shows about Mounjaro and sexual function, compares it with Wegovy (semaglutide), and clarifies why weight loss medications may indirectly affect intimacy through metabolic and psychological changes. If you're considering prescription weight loss treatment, understanding potential effects on sexual health is part of making an informed decision with your GP or prescriber.
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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.
Mounjaro vs Wegovy — Clinical Trial Evidence on Sexual Function
Neither Mounjaro nor Wegovy lists sexual dysfunction as a common side effect in their UK clinical trial data. In the SURMOUNT-1 trial for Mounjaro (tirzepatide), libido changes were not reported as a primary or secondary outcome. Similarly, the STEP trials for Wegovy (semaglutide) did not identify sexual dysfunction as a frequent adverse event. Both medications work as GLP-1 receptor agonists — Mounjaro uses a dual GIP+GLP-1 mechanism, while Wegovy is GLP-1 only. Neither mechanism directly targets sexual function pathways. However, individual experiences vary widely. Some users report improved sexual confidence linked to weight loss and improved body image, whilst others report fatigue or reduced libido as part of broader side effects like nausea or appetite suppression. These indirect effects are typically dose-dependent and often improve as the body adjusts.
- SURMOUNT and STEP trials: sexual dysfunction not reported as common side effect
- Both medications work on appetite and metabolism, not directly on sexual function
- Weight loss itself may improve sexual confidence and function for some people
- Side effects like nausea or fatigue may indirectly reduce libido temporarily
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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.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
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Why Weight Loss Medications May Indirectly Affect Intimacy
Weight loss medications affect libido indirectly through several pathways. Metabolic changes — reduced appetite and nutrient absorption can temporarily lower energy levels, affecting sexual desire. Psychological factors — improved body image and confidence after weight loss often enhances sexual function and satisfaction. Medication side effects — nausea, fatigue, or gastrointestinal discomfort may suppress interest in intimacy, though these typically diminish over weeks or months. Additionally, managing a new medication routine and lifestyle changes can affect mood and stress levels. Weight-related conditions like type 2 diabetes, high blood pressure, and sleep apnoea are known to reduce sexual function independently; treating these conditions through weight loss may actually improve sexual health. If you experience persistent changes in sexual function after starting Mounjaro, discussing this with your GP or prescriber is important — it may indicate a need for dose adjustment, additional support, or investigation of underlying factors.
- 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 cause erectile dysfunction or reduced libido?
Erectile dysfunction is not listed as a common side effect of Mounjaro in UK clinical trials. However, related side effects like fatigue, nausea, or appetite suppression might indirectly reduce sexual interest in some people. These effects are typically temporary and often improve as your body adjusts to the medication. Always discuss any concerns with your GP.
Is Wegovy more likely to affect sexual function than Mounjaro?
No — both Mounjaro and Wegovy show similar patterns in clinical data, with sexual dysfunction not reported as a common side effect. Individual experiences vary. Differences in how people respond are more related to personal metabolism, dose tolerance, and psychological factors than the medication itself.
Can weight loss from Mounjaro or Wegovy improve sexual function?
Yes, for many people. Weight loss itself can improve sexual confidence, reduce joint pain, lower blood pressure, and enhance overall wellbeing — all of which support better sexual function. Additionally, treating weight-related conditions like type 2 diabetes may improve sexual health independently of the medication.
Should I stop Mounjaro if I experience changes in libido?
Do not stop your medication without guidance from your prescriber. Changes in libido are usually temporary and improve as your body adjusts. Your GP or prescriber can assess whether the change is related to Mounjaro, adjust your dose, or explore other factors. Open discussion is essential for safe management.
Are there other UK weight loss medications I should consider if sexual function is a concern?
Both Mounjaro and Wegovy show similar safety profiles regarding sexual function in clinical data. If you have specific health concerns, your GP can assess your individual suitability for either medication through a clinical assessment. Other lifestyle and medical factors matter more than choice between these two medications.
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.