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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Does Mounjaro Affect Libido?
Mounjaro (tirzepatide) is a prescription-only weight management injection that may affect sexual function in some people, though this is not a common reported side effect. This guide explains what the evidence shows, how Mounjaro works, and when to speak with your GP. If you're considering Mounjaro, understanding potential effects on sexual health is an important part of making an informed decision about whether this medication is right for you.
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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.
What the Evidence Shows About Mounjaro and Libido
Sexual dysfunction and changes in libido are not listed as common side effects in the official Mounjaro product information. However, sexual health can be indirectly affected by several factors related to how Mounjaro works and the experience of using it.
Indirect effects on libido may include:
- Nausea and digestive symptoms — very common side effects that may reduce sexual interest temporarily, particularly in the first few weeks of treatment
- Fatigue and low energy — reported by some people, which can naturally reduce sexual desire
- Psychological factors — gradual weight management and improved body image may positively affect sexual confidence and function for some people
- Blood sugar regulation — improving blood sugar control in people with prediabetes or type 2 diabetes may improve sexual function, as high blood sugar can damage blood vessels
Unlike some other weight loss medications, changes in libido are not a recognised direct pharmacological effect of tirzepatide. The dual GIP and GLP-1 mechanism works on appetite and metabolic pathways, not sex hormone regulation.
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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.
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What to Do If You Have Concerns About Sexual Function
If you experience any changes in sexual function or libido after starting Mounjaro, tell your GP or the prescriber managing your treatment. Changes in sexual desire can occasionally be a sign of depression or mood changes, which may require support. It's also worth considering whether other factors — such as nausea, fatigue, stress, or relationship issues — might be contributing. Your prescriber can help you work out whether the changes are related to Mounjaro itself or to other factors, and whether continuing the medication is right for you. Sexual health is part of overall health, and it's important to discuss it openly with your healthcare team.
- 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.
Is sexual dysfunction a common side effect of Mounjaro?
No. Sexual dysfunction is not listed as a common side effect of Mounjaro in the UK product information. However, some people may experience indirect effects on sexual function through fatigue, nausea, or improved confidence from weight loss.
Can Mounjaro directly affect sex hormones?
No. Mounjaro (tirzepatide) works as a GIP and GLP-1 receptor agonist, affecting appetite and metabolism. It does not directly interact with sex hormone pathways like testosterone or oestrogen.
Could improved health from weight loss improve sexual function?
Yes, potentially. Weight loss and improved blood sugar control can improve cardiovascular health and blood vessel function, both of which support healthy sexual function. Improved body image and confidence may also help.
Should I stop Mounjaro if I notice changes in libido?
Do not stop without speaking to your GP first. Tell your prescriber about any changes in sexual function. They can help determine whether it's related to Mounjaro, other factors, or medication dose — and discuss options with you.
What other Mounjaro side effects might indirectly affect libido?
Nausea, constipation, diarrhoea, and fatigue are common in the first few weeks and may reduce sexual interest temporarily. These usually improve as your body adjusts to the medication. Using our GLP-1 weight loss calculator can help you understand what to expect with treatment.
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.