Fertility, pregnancy and weight loss medicines: how to time it

SASian Anderson, Writer and editor, MyGLP. Sources checked 21 October 2026.

The stop dates

The reason for the gap is simple. The medicines were never tested in pregnant women, and animal studies raised enough doubt that the regulators ruled them out. The UK Teratology Information Service leaflet on GLP-1 medicines sets out what is and is not known.

Why losing weight first can help

Carrying extra weight makes it harder to conceive and raises the risk of problems in pregnancy, from gestational diabetes to high blood pressure. The NHS pre-pregnancy advice covers weight alongside folic acid and stopping smoking. Many women use a weight loss medicine for a stretch, stop on the schedule above, then try. If you have PCOS, weight loss can restart ovulation on its own, which is one reason the medicines are popular with women who have struggled to conceive. See PCOS and weight loss medicines.

Fertility clinics have their own rules. Some ask for a BMI under 30 or 35 before IVF. Ask the clinic how long before treatment they want the medicine stopped, since it may be longer than the leaflet gap.

If you find out you are pregnant on the medicine

1. Stop the medicine. Do not take the next dose.
2. Tell your GP or midwife at your first contact, and say which medicine, which dose and when you last took it.
3. Start folic acid if you have not already. The NHS dose is 400 micrograms a day, or 5mg a day if your BMI is 30 or over, which needs a prescription.
4. Do not blame yourself. Ovulation can return without warning and the pill can absorb less on Mounjaro. Thousands of women have been in the same place.

The published reports so far on pregnancies that began on a GLP-1 medicine have not shown a clear pattern of harm, but the numbers are small. Your midwife may offer extra scans. The medicines in pregnancy leaflet is the plain-language summary to read.

Weight gain in pregnancy after stopping

Appetite comes back when the medicine stops, and pregnancy adds to it. There is no UK guideline that sets a target weight gain in pregnancy, and the NHS does not recommend dieting while pregnant. Aim for the same balanced plate you built on the medicine: protein at each meal, vegetables, fibre, and water. Our protein guide still applies, with a bigger plate.

Breastfeeding

The NHS says tirzepatide is not used while breastfeeding because it is not known whether the medicine passes into milk. The Wegovy leaflet says the same for semaglutide. Prescribers will not restart a weight loss medicine until you have stopped feeding. The pharmacy consultation form asks about breastfeeding for this reason, so answer it honestly.

Planning the restart

After the baby arrives and feeding has ended, you can go back through a pharmacy consultation. You start again at the first dose, Step 1, whatever dose you were on before. The price of Step 1 is the lowest in the schedule. Compare the Step 1 prices when you are ready.

Sources

1. Tirzepatide: pregnancy and breastfeeding (NHS)
2. Wegovy patient information leaflet (Novo Nordisk, via the electronic medicines compendium)
3. GLP-1 receptor agonists in pregnancy (UK Teratology Information Service (bumps))
4. Planning your pregnancy (NHS)