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
Can Mounjaro Affect Your Fertility?
No current evidence suggests that Mounjaro (tirzepatide) causes infertility in either men or women. However, because Mounjaro is a relatively new weight management medication, fertility data remains limited. What is clear is that Mounjaro is not recommended during pregnancy or when trying to conceive. If you're considering Mounjaro and fertility is important to you, it's essential to discuss your plans with your GP or a licensed prescriber before starting treatment. They can assess your individual circumstances and recommend the safest approach for your situation.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 the Evidence Shows About Mounjaro and Fertility
Tirzepatide (Mounjaro's active ingredient) has not been shown to damage fertility or reproductive function in clinical trials. The SURMOUNT weight management trials did not identify infertility as a side effect in either sex. However, there are important considerations:
- Weight loss itself improves fertility: Excess weight can reduce fertility in both men and women; losing weight often improves reproductive health and hormone balance
- Pregnancy is not recommended: Mounjaro is contraindicated in pregnancy because it may affect fetal development — this is a precaution, not evidence of infertility
- Limited long-term data: Tirzepatide is newer than some alternatives like semaglutide (Wegovy); longer-term reproductive safety data will accumulate over time
- Individual factors matter: Your fertility depends on many factors — age, existing health conditions, partner factors, and underlying causes of excess weight
The MHRA (UK Medicines and Healthcare Products Regulatory Agency) has approved Mounjaro with standard fertility and pregnancy warnings, but no specific infertility risk has been identified.
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.
Mounjaro, Pregnancy Planning, and Your GP
If you're planning to become pregnant or already are, Mounjaro is not suitable and you should stop taking it immediately and inform your GP. Women using oral contraceptives should add a barrier method or switch to a non-oral contraceptive for 4 weeks after starting Mounjaro and 4 weeks after each dose increase, because GLP-1 medications may reduce the absorption of oral contraceptives.
Before starting Mounjaro, tell your prescriber if you're planning to conceive within the next year. Your GP can discuss whether Mounjaro is appropriate for you right now, or whether timing adjustments would be safer. They may recommend a different approach, like lifestyle changes first, or an alternative weight loss strategy if pregnancy is imminent.
- 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. Clinical trials have not identified infertility as a side effect of tirzepatide. However, Mounjaro should not be used during pregnancy or when actively trying to conceive. If you're concerned about fertility, discuss your situation with your GP before starting Mounjaro.
Will Mounjaro affect my ability to get pregnant?
There is no evidence that Mounjaro reduces your ability to conceive. In fact, weight loss from Mounjaro may improve fertility in some people, as excess weight can reduce reproductive function. Always inform your prescriber if you're planning pregnancy.
Can I use Mounjaro if I'm trying for a baby?
No. Mounjaro should not be used when you're actively trying to conceive or if you're pregnant. It may affect fetal development. If pregnancy is planned within a year, discuss safer alternatives with your GP before starting Mounjaro.
What contraception should I use with Mounjaro?
If you use an oral contraceptive pill, add a barrier method or switch to a non-oral option for 4 weeks after starting Mounjaro and after each dose increase. Mounjaro may reduce pill absorption. Discuss contraception options with your GP or prescriber.
Does weight loss from Mounjaro improve fertility?
Yes, for many people. Excess weight can reduce fertility in both men and women by affecting hormone balance and ovulation. Losing weight through Mounjaro — or any method — often improves reproductive health and increases conception chances.
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.