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 Affect Fertility?
Mounjaro (tirzepatide) is a prescription-only weight management injection available in the UK. If you're considering pregnancy or worried about your fertility while using Mounjaro, it's important to understand what the evidence shows. Current clinical data suggests Mounjaro does not directly damage fertility in either women or men, but there are important considerations around timing, pregnancy planning, and medical supervision that you need to discuss with your GP before making any decisions about your treatment.
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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.
What the Evidence Shows About Mounjaro and Fertility
There is no clinical evidence that tirzepatide (the active ingredient in Mounjaro) directly damages fertility or reproductive function in women or men. Tirzepatide works by activating GIP and GLP-1 receptors in the body to help regulate appetite and support weight management — these mechanisms do not target reproductive organs or hormones.
However, Mounjaro is not recommended during pregnancy. Animal studies have shown potential effects on fetal development at high doses, and it has not been adequately studied in pregnant women. If you become pregnant while taking Mounjaro, you should contact your GP immediately and stop the injection.
Weight loss itself may actually improve fertility outcomes in people with obesity, as excess weight can affect hormone balance and ovulation. Our GLP-1 weight loss calculator can help you understand potential weight changes, which may support your fertility goals alongside medical guidance.
Clinically BackedWeight Loss
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Planning Pregnancy and Mounjaro — What You Need to Know
If you're planning to become pregnant, inform your GP or prescriber before starting Mounjaro. Current guidance recommends stopping tirzepatide at least 2 months before you plan to conceive, though your individual circumstances may differ.
Women taking Mounjaro should use reliable contraception while on treatment. Mounjaro may reduce the absorption of oral contraceptives — discuss alternative contraception options with your GP.
For men, there is no evidence that Mounjaro reduces fertility, but discuss your weight management goals and medication use with your healthcare provider if you're planning fatherhood.
Always consult your GP or specialist prescriber before making any changes to your Mounjaro treatment when considering pregnancy or fertility concerns.
- 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 infertility?
No. There is no clinical evidence that Mounjaro (tirzepatide) directly damages fertility in women or men. However, it is not recommended during pregnancy, and you should stop treatment at least 2 months before attempting to conceive. Always consult your GP before starting or stopping any weight management medication.
Can I take Mounjaro if I'm trying to get pregnant?
Not during pregnancy itself. If you're planning to conceive, discuss this with your prescriber — you'll typically be advised to stop Mounjaro 2 months beforehand. Weight loss before pregnancy may actually improve fertility outcomes in people with obesity, supporting your goals.
Will Mounjaro affect my contraception?
Mounjaro may reduce how well oral contraceptive pills are absorbed, reducing their effectiveness. If you take the contraceptive pill, discuss alternative contraception methods with your GP, such as barrier methods or long-acting reversible contraception (LARC).
What if I become pregnant while taking Mounjaro?
Stop the injection immediately and contact your GP. While animal studies haven't shown severe harm at therapeutic doses, tirzepatide has not been adequately tested in pregnant women. Your GP can assess your individual situation and advise on safe next steps.
Does weight loss from Mounjaro improve fertility?
Yes, weight loss may improve fertility outcomes. Excess weight can affect hormone balance and ovulation. If you're overweight or obese and experiencing fertility issues, Mounjaro alongside lifestyle changes may support your health goals — discuss this with your GP or fertility specialist.
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.