Mounjaro (tirzepatide) is a once-weekly injection licensed in the UK for managing type 2 diabetes in adults. As a dual GIP and GLP-1 receptor agonist, it improves blood glucose control and often leads to significant weight loss. For individuals planning to start a family, questions naturally arise about whether Mounjaro affects fertility. Whilst there are no dedicated human studies examining tirzepatide's direct effects on reproductive function, important considerations exist around weight changes, contraception requirements, and pregnancy planning. This article explores the current evidence on Mounjaro and fertility in both women and men, and provides guidance on discussing reproductive plans with your healthcare provider.

Understanding Mounjaro and Its Primary Uses

Mounjaro (tirzepatide) is a prescription medication licensed in the UK for the treatment of type 2 diabetes mellitus in adults. It belongs to a novel class of medicines known as dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonists. By mimicking the action of these naturally occurring incretin hormones, Mounjaro helps regulate blood glucose levels, enhances insulin secretion when blood sugar is elevated, and reduces glucagon release.

Administered as a once-weekly subcutaneous injection, Mounjaro offers a treatment option for individuals whose diabetes is inadequately controlled with diet, exercise, and other oral antidiabetic medications. Clinical trials have demonstrated that tirzepatide significantly improves glycaemic control, as measured by reductions in HbA1c levels, and promotes substantial weight loss—an important benefit given the strong association between obesity and type 2 diabetes.

While Mounjaro is primarily indicated for diabetes management, its effects on weight have generated interest in its potential broader metabolic benefits. The Medicines and Healthcare products Regulatory Agency (MHRA) and the European Medicines Agency (EMA) have approved tirzepatide specifically for glycaemic control in adults with type 2 diabetes.

Common side effects include gastrointestinal symptoms such as nausea, vomiting, diarrhoea, and decreased appetite, which are typically mild to moderate and tend to diminish over time. Important safety warnings include risk of pancreatitis (seek urgent medical attention for severe, persistent abdominal pain with or without vomiting), gallbladder disease, dehydration from persistent vomiting or diarrhoea, and potential worsening of diabetic retinopathy with rapid improvement in blood glucose. When used with insulin or sulfonylureas, Mounjaro may increase the risk of hypoglycaemia, and dose adjustments of these medications may be needed.

If you experience any suspected side effects, report them via the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk).

Does Mounjaro Affect Fertility in Women?

The effects of Mounjaro on human fertility are unknown, as there are no dedicated human studies examining this specific aspect. Animal studies do not indicate direct harm to fertility at clinically relevant exposures, but human data remain limited.

One important consideration is that significant weight loss—a common effect of Mounjaro treatment—can influence reproductive hormones and menstrual cycles. In women with polycystic ovary syndrome (PCOS) or obesity-related anovulation, weight reduction may potentially improve fertility by restoring more regular ovulation and hormonal balance. Conversely, rapid or excessive weight loss can occasionally disrupt menstrual cycles in some individuals, though this is generally a temporary effect. It's important to note that Mounjaro is not licensed for the treatment of PCOS or fertility issues.

Mounjaro is not recommended during pregnancy. Animal studies have shown potential risks to the developing foetus, and there is insufficient data on the safety of tirzepatide in pregnant women. The Summary of Product Characteristics (SmPC) advises that women of childbearing potential should use effective contraception during treatment and for at least four weeks after discontinuing Mounjaro. This precautionary period allows the medication to be cleared from the body before conception.

It is also important to note that Mounjaro may reduce the effectiveness of oral contraceptives, particularly during the initial weeks of treatment or after dose increases, due to delayed gastric emptying. Women using oral contraceptives should use a non-oral contraceptive method or add a barrier method for 4 weeks after starting Mounjaro and for 4 weeks after each dose escalation.

Mounjaro is not recommended during breastfeeding. You should decide whether to discontinue breastfeeding or discontinue tirzepatide treatment, taking into account the benefits of breastfeeding for your child and the benefits of treatment for you.

If you are planning to conceive, discuss your treatment plan with your GP or diabetes specialist well in advance. They can advise on the appropriate timing to discontinue Mounjaro and ensure optimal glycaemic control through alternative medications that are safe during pregnancy, such as insulin or metformin.

Consult your GP if you experience menstrual periods stopping for more than 3 months, if your cycles become very irregular, or if you have been trying to conceive without success for 12 months (or 6 months if you are 35 or older).

What to Discuss with Your Healthcare Provider

Open communication with your healthcare provider is essential when considering Mounjaro treatment, particularly if you have concerns about fertility or are planning a pregnancy. Before starting Mounjaro, inform your doctor about your reproductive plans, current contraceptive methods, menstrual cycle regularity, and any history of fertility issues or gynaecological conditions such as PCOS.

Your healthcare provider should conduct a thorough assessment of your diabetes management needs and discuss the risks and benefits of tirzepatide in the context of your individual circumstances. This includes reviewing your current medications, as some drug interactions may affect treatment efficacy or safety. For women of childbearing age, your doctor will emphasise the importance of reliable contraception throughout treatment and explain the recommended washout period before attempting conception.

Key questions to raise with your healthcare provider include:

• How long should I wait after stopping Mounjaro before trying to conceive?

• What alternative diabetes medications are safe during pregnancy planning and pregnancy?

• Could Mounjaro's effects on my weight positively or negatively influence my fertility?

• What additional contraceptive measures should I take if I'm using oral contraceptives? (Remember to use a non-oral method or add a barrier method for 4 weeks after starting and for 4 weeks after each dose increase)

• How will my diabetes be managed if I need to discontinue Mounjaro for pregnancy?

Your doctor may also recommend preconception counselling with a specialist diabetes team. This should include optimising your HbA1c (individualised targets, often <48 mmol/mol if achievable safely), prescribing high-dose folic acid (5 mg daily) to take before conception and until 12 weeks of pregnancy, reviewing all medications, and arranging retinal and renal assessments. Achieving optimal glycaemic control before conception significantly reduces the risk of complications for both mother and baby.

If you discover you are pregnant while taking Mounjaro, stop the medication immediately and contact your healthcare provider urgently. Your doctor will arrange a prompt review to transition you to pregnancy-safe diabetes management (such as insulin) and provide appropriate referrals for specialist antenatal care.

Does Mounjaro Affect Fertility in Men?

There is currently no evidence from clinical trials to date of a direct adverse effect on male fertility with Mounjaro use. However, human data are limited and specific studies examining tirzepatide's effects on male reproductive function are lacking. Unlike some medications that can influence hormonal pathways involved in spermatogenesis, the effects of GLP-1 and GIP receptor agonists on the male reproductive system have not been extensively studied.

However, as with women, weight loss associated with Mounjaro treatment may have indirect effects on male reproductive health. Obesity is associated with reduced testosterone levels, erectile dysfunction, and decreased sperm quality. For men with obesity-related hypogonadism, significant weight reduction may potentially improve testosterone levels and sexual function, which could indirectly enhance fertility. Studies of weight loss generally (not specific to tirzepatide) have shown improvements in sperm parameters, including sperm count, motility, and morphology in overweight and obese men.

Men taking Mounjaro who are planning to father a child should still discuss their treatment with their healthcare provider, particularly if they have pre-existing fertility concerns or other medical conditions that might affect reproductive health. While there is no official requirement for men to discontinue Mounjaro before attempting conception with their partner, maintaining good diabetes control is important for overall health and wellbeing.

Men should contact their GP if they experience:

• Persistent erectile dysfunction or reduced libido

• Significant unexplained weight loss beyond expected treatment effects

• Any concerns about fertility or reproductive health

• Inability to conceive after 12 months of trying (or 6 months if female partner is 35 or older)

It is worth noting that good glycaemic control itself is important for male fertility. Poorly controlled diabetes can lead to erectile dysfunction, retrograde ejaculation, and DNA damage in sperm. Therefore, effective diabetes management may indirectly support reproductive health by improving metabolic parameters and reducing diabetes-related complications.

Frequently Asked Questions