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 Your Fertility?
Mounjaro (tirzepatide) is not known to directly affect fertility in either men or women. However, because it's a prescription-only weight management injection, there are important considerations if you're planning pregnancy. Significant weight loss itself can improve fertility outcomes in people with obesity, but Mounjaro must be stopped before conception. If you're considering pregnancy, discuss your plans with your GP or the prescriber managing your 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 the Evidence Shows About Mounjaro and Fertility
Clinical trial data: The SURMOUNT clinical trials that led to Mounjaro's UK approval did not identify fertility problems as a side effect. Mounjaro works as a dual GIP and GLP-1 receptor agonist, signalling to the brain to reduce appetite and supporting weight loss alongside diet and exercise changes.
No direct mechanism affecting reproductive hormones: Unlike some medications, Mounjaro does not directly interfere with hormones that regulate the menstrual cycle or sperm production. However, significant weight loss itself can influence reproductive health — sometimes positively, by improving ovulation regularity in people with polycystic ovary syndrome (PCOS) or other weight-related fertility issues.
- Weight loss of 5–10% can improve menstrual regularity and ovulation in people with obesity
- Mounjaro's weight loss effect may indirectly benefit fertility in this way
- Individual responses vary significantly
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 and Pregnancy — Important Safety Information
Mounjaro must be stopped before pregnancy. The medicine is not tested for safety in pregnancy, and animal studies suggest potential risks to a developing baby. The UK prescribing information recommends stopping Mounjaro at least 3 months before trying to conceive.
If you take an oral contraceptive, Mounjaro may reduce its effectiveness — your prescriber will advise adding a barrier method or switching contraception during treatment and for 4 weeks after starting or increasing your dose. If you become pregnant unexpectedly while taking Mounjaro, contact your GP immediately. Plan your fertility and pregnancy timing with your healthcare team from the start of treatment.
- 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 men taking Mounjaro father children?
Yes. Mounjaro has not been shown to affect male fertility or sperm production. However, if you're planning to father a child, discuss this with your prescriber as Mounjaro should be managed carefully alongside fertility planning. Weight loss achieved with Mounjaro may improve overall health outcomes.
Does Mounjaro stop periods or affect the menstrual cycle?
Not directly. Mounjaro does not typically cause period changes. However, gradual weight management can temporarily affect menstrual regularity in some people. If you notice significant changes to your cycle, report this to your GP. For most people, weight loss improves cycle regularity if obesity was affecting it.
Can I take Mounjaro if I'm trying to get pregnant?
No. Stop Mounjaro at least 3 months before trying to conceive. It's not tested for safety in early pregnancy. If you're planning pregnancy, discuss timing with your prescriber. Weight loss before conception may actually improve fertility outcomes in people with obesity.
What should I do if I become pregnant while taking Mounjaro?
Contact your GP immediately. Do not stop Mounjaro abruptly, but discuss next steps with your healthcare team. Early pregnancy loss while on Mounjaro is not established as a risk, but the medicine should be stopped under medical guidance. Your GP can advise on safe management.
Does Mounjaro affect contraception effectiveness?
Yes — Mounjaro may reduce the absorption of oral contraceptives (the contraceptive pill). If you're on the pill, your prescriber will recommend adding a barrier method or switching to a different contraceptive. This applies for 4 weeks after starting Mounjaro and 4 weeks after each dose increase.
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.