Pregnancy and
GLP-1 Medications

Why GLP-1 medications are contraindicated in pregnancy

The MHRA and the manufacturers of both Wegovy (semaglutide) and Mounjaro (tirzepatide) explicitly state that these medications must not be used during pregnancy. This contraindication is based on preclinical data rather than human safety studies, as pregnant women are excluded from clinical trials for ethical reasons.

What preclinical studies showed

Animal studies conducted as part of the regulatory approval process have provided the basis for current safety warnings:

• Semaglutide: Animal reproduction studies in rats and rabbits showed adverse effects on embryonic and foetal development at doses relevant to the human therapeutic range. Effects included reduced foetal growth, skeletal abnormalities and increased pregnancy loss.
• Tirzepatide: Similar findings in animal studies, including reduced foetal body weight and skeletal variations. Embryotoxicity was observed at doses comparable to the maximum recommended human dose.

It is important to note that animal data does not always predict human outcomes. However, in the absence of human safety data, the precautionary principle applies. The BNF and MHRA SmPC (Summary of Product Characteristics) for both drugs clearly state that use during pregnancy should be avoided.

How long to wait before trying to conceive

The recommended washout period differs between semaglutide and tirzepatide based on their pharmacokinetic properties — specifically, how long the drug remains active in the body after the last dose.

These washout periods ensure that the drug has been substantially eliminated from the body before conception occurs. The two-month recommendation for semaglutide reflects its longer half-life, meaning it takes longer to clear from the system.

The fertility factor: weight loss and unplanned pregnancy

An important and sometimes overlooked consequence of GLP-1-mediated weight loss is its effect on fertility. Obesity is associated with hormonal imbalances that can impair ovulation and reduce fertility. Significant weight loss can reverse these changes, leading to improved ovulatory function and increased chance of conception.

Polycystic ovary syndrome (PCOS)

Women with PCOS, a condition affecting an estimated 1 in 10 women of reproductive age in the UK, are particularly affected. Weight loss of 5–10 per cent can be sufficient to restore regular ovulation. GLP-1 medications often produce weight loss well beyond this threshold, potentially restoring fertility in women who had previously been subfertile.

Oral contraceptive effectiveness

GLP-1 medications slow gastric emptying, which can theoretically affect the absorption of oral medications, including oral contraceptive pills. Whilst clinical evidence specifically linking GLP-1 therapy to oral contraceptive failure is limited, the BNF notes this potential interaction. Women taking oral hormonal contraception alongside GLP-1 medications should:

• Discuss alternative or additional contraceptive methods with their GP or family planning clinic
• Consider non-oral methods such as intrauterine devices (IUDs), contraceptive implants or injectable contraception
• Be aware that vomiting (a common GLP-1 side effect) can reduce oral contraceptive effectiveness

What if you become pregnant whilst on a GLP-1 medication?

If you discover you are pregnant whilst taking semaglutide or tirzepatide, the recommended steps are:

1. Stop the medication immediately — do not take another dose
2. Contact your GP or midwife as soon as possible to inform them of the exposure
3. Do not panic — accidental exposure in early pregnancy, whilst not ideal, does not necessarily mean harm has occurred
4. Request early pregnancy monitoring — your antenatal care team may recommend additional ultrasound scans

Post-marketing surveillance data from semaglutide use in the general population is beginning to accumulate, but it is still insufficient to draw definitive conclusions about human pregnancy outcomes. Reports from the Novo Nordisk pregnancy registry and pharmacovigilance databases are ongoing. The MHRA continues to monitor this data.

Breastfeeding and GLP-1 medications

The MHRA SmPC for both semaglutide and tirzepatide states that breastfeeding is not recommended during treatment. The rationale is straightforward: there is no human data on whether these drugs pass into breast milk or, if they do, in what concentrations.

What we know

• Animal data: Semaglutide has been detected in the milk of lactating rats. Tirzepatide data in lactating animals is limited.
• Human data: No published studies on excretion into human breast milk for either medication
• Theoretical risk: GLP-1 analogues are large peptide molecules, which generally have low oral bioavailability. Even if present in breast milk, absorption by the infant may be minimal. However, this has not been confirmed in clinical studies.

Until human data becomes available, the precautionary recommendation remains not to breastfeed whilst taking GLP-1 medications. Women who have recently stopped a GLP-1 medication should observe the relevant washout period before initiating breastfeeding.

Obesity management during pregnancy

For women who discontinue GLP-1 therapy to become pregnant, the question of weight management during pregnancy becomes relevant. NICE guideline CG189 (weight management before, during and after pregnancy) recommends:

• Women should not attempt to lose weight during pregnancy
• A balanced, nutrient-dense diet is recommended throughout pregnancy
• Physical activity during pregnancy is encouraged unless medically contraindicated
• Women with a BMI of 30 or above should be offered referral to a dietitian
• Gestational weight gain should be monitored and managed appropriately

Women who have achieved significant weight loss on GLP-1 therapy before pregnancy may be concerned about weight regain. Maintaining healthy eating habits and appropriate physical activity levels during pregnancy can help, but the priority must be adequate nutrition for foetal development.

After pregnancy: restarting GLP-1 medication

Following pregnancy, women may wish to resume GLP-1 therapy for weight management. Key considerations include:

• Breastfeeding: GLP-1 medications should not be started until breastfeeding has ceased
• Postnatal recovery: Discuss timing with your GP or prescriber; most clinicians recommend waiting until the routine 6–8 week postnatal check
• Dose re-escalation: If restarting after a break, the standard dose-escalation protocol should be followed from the beginning to minimise gastrointestinal side effects
• Mental health: Postnatal depression and anxiety should be screened for; the appetite-suppressing effects of GLP-1 medications may interact with postnatal mood disturbances

Frequently asked questions

Can I take Wegovy whilst trying to get pregnant?

No. The MHRA SmPC states that semaglutide should be stopped at least two months before planned conception. If you are actively trying to conceive, you should not be taking Wegovy.

Is there any GLP-1 medication that is safe in pregnancy?

No GLP-1 medication is currently approved for use during pregnancy. This applies to semaglutide, tirzepatide, liraglutide and all other drugs in this class. The contraindication is consistent across all GLP-1 receptor agonists.

I became pregnant on Wegovy. Will my baby be harmed?

Accidental early exposure does not necessarily mean harm will occur. However, you should stop the medication immediately and inform your GP or midwife. Your antenatal care team will advise on any additional monitoring that may be appropriate. Human data on first-trimester exposure is limited but growing.

Can GLP-1 medication affect male fertility?

Current evidence does not suggest a significant adverse effect of GLP-1 medications on male fertility. Some preclinical data has raised theoretical concerns about effects on sperm quality, but human studies have not confirmed a clinically meaningful impact. Men taking GLP-1 medications who are planning to have children should discuss any concerns with their prescriber.