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 Cause Infertility?
Mounjaro (tirzepatide) does not directly cause infertility based on current evidence. However, there are important considerations for anyone planning pregnancy or currently trying to conceive. If you're considering this prescription-only weight loss injection, it's essential to understand how it affects fertility and pregnancy planning before starting 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 trials and post-marketing data show no direct link between tirzepatide (Mounjaro) and infertility in either men or women. The medication works as a dual GIP and GLP-1 receptor agonist, affecting appetite regulation and blood sugar control — not reproductive hormones directly.
However, several important points apply:
- Weight loss itself improves fertility: Losing 5–10% of body weight can restore regular menstrual cycles and improve ovulation in women with polycystic ovary syndrome (PCOS) and obesity-related infertility. For men, weight loss improves sperm quality.
- Gastrointestinal effects may reduce medication absorption: Mounjaro slows gastric emptying, which could theoretically affect absorption of oral contraceptives or other medications taken simultaneously — though this is rare with weekly injections.
- Pregnancy is not recommended during Mounjaro treatment: The UK product information advises women to avoid pregnancy while taking Mounjaro and for 12 weeks after stopping.
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.
Planning Pregnancy While on Mounjaro
If you're taking Mounjaro and planning to conceive, discuss this with your GP or the prescriber managing your weight loss. You'll typically need to stop Mounjaro at least 12 weeks before trying to conceive, allowing the medication to clear your system and your body to stabilise.
The weight loss achieved on Mounjaro often persists after stopping — meaning you may retain fertility benefits even after discontinuing the injection. For women taking oral contraceptives, add a barrier method for 4 weeks after starting Mounjaro and 4 weeks after each dose increase, as the injection may reduce oral medication absorption. Men's fertility is not affected by these precautions. Always inform your prescriber of pregnancy plans before starting 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.
Does Mounjaro cause infertility?
No — tirzepatide does not directly cause infertility. However, pregnancy is not recommended during treatment. Discuss pregnancy plans with your GP before starting Mounjaro, as you'll typically need to stop 12 weeks before conceiving.
Can men take Mounjaro if they're trying to have children?
Yes. Mounjaro does not affect male fertility or sperm quality. In fact, weight loss may improve sperm parameters. Men can continue Mounjaro while trying to conceive, but should inform their partner and healthcare provider of pregnancy plans.
Does Mounjaro affect oral contraceptives?
Mounjaro may reduce absorption of oral contraceptives. The UK guidance recommends using a barrier method (condoms) for 4 weeks after starting Mounjaro and 4 weeks after each dose increase if relying on the pill for contraception.
How long after stopping Mounjaro can I try to conceive?
The UK product information recommends waiting at least 12 weeks after your last Mounjaro dose before trying to conceive. This allows the medication to fully clear your system. Your GP can advise based on your individual health.
Will I lose the weight loss benefits if I stop Mounjaro to get pregnant?
Not necessarily. Weight lost during Mounjaro treatment often persists after stopping the injection, especially if you maintain healthy eating and activity habits. Many people continue their healthy lifestyle after treatment ends, helping preserve weight loss gains.
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.