Retatrutide and Pregnancy: Fertility, Birth Control and Breastfeeding

There's no human data on retatrutide and pregnancy: no study has published a single pregnancy on it, so nobody can say how risky it is. The closest guidance comes from its relatives: the tirzepatide and semaglutide labels say to stop when a pregnancy is recognized, and the Wegovy label says to stop at least 2 months before a planned one. How long to wait before trying, whether the pill still works and whether breastfeeding is safe have no retatrutide answer yet, so each answer below comes from the nearest evidence and says which drug it's from.

Six Phase 3 trials have reported results as of October 2026, but no approved version of retatrutide exists, and so no label. A label is where pregnancy, contraception and breastfeeding advice normally lives. Here is that advice from the labels and regulators that cover the closest drugs. For the wider picture, see is retatrutide safe.

What's known about retatrutide and pregnancy

Almost nothing, by design. The Phase 2 obesity trial's ClinicalTrials.gov listing kept out women who were pregnant, breastfeeding or planning a pregnancy, and women who could get pregnant and weren't using adequate contraception. The eligibility text on the registry's Phase 3 listings, TRIUMPH-1 among them, doesn't mention pregnancy at all (we checked on October 31, 2026), and we couldn't find the full protocols.

So the evidence is class evidence. Tirzepatide's Zepbound label puts it plainly: "Weight loss offers no benefit to a pregnant patient and may cause fetal harm." It tells people to stop when a pregnancy is recognized and says the human data are too thin to judge the risk of birth defects or miscarriage. The fetal-harm concern comes from pregnant lab animals, where tirzepatide slowed fetal growth at exposures like those in people and, in one of two species, caused fetal abnormalities. The label notes the mothers were also eating less and losing weight. It hasn't been tested in people.

The human data that do exist cover GLP-1 drugs as a class. A 2024 study in JAMA Internal Medicine followed 938 babies whose mothers, all with type 2 diabetes, filled a GLP-1 prescription from 90 days before pregnancy to the end of the first trimester. Major birth defects showed up in 8.3% of them, against 7.8% of babies exposed to insulin, an adjusted relative risk of 0.95 (95% CI 0.72 to 1.26). That's no sign of a big increase, though the interval can't rule out a small one. It says nothing about retatrutide's third target, the glucagon receptor, which no pregnancy study has covered.

For scale, the Zepbound label gives the US background risk in recognized pregnancies as 2% to 4% for major birth defects and 15% to 20% for miscarriage, before any drug is involved.

How long before trying to conceive should you stop?

No regulator has set a number for retatrutide. What drives these intervals is half-life, the time it takes the body to clear half the drug, and retatrutide's is about 6 days, per its Phase 1b trial in The Lancet, next to tirzepatide's 5 to 6 days. Lilly Medical Information puts peak blood levels 12 to 72 hours after a dose, which is why one weekly shot works (more on the retatrutide half-life).

The Wegovy label ties its 2 months to semaglutide's long half-life and says the drug stays in the blood for about 5 to 7 weeks after the last dose. The chart applies the same math to retatrutide's half-life.

Lilly's own trial-entry rule isn't pregnancy advice, but it shows how Lilly thinks about washout. Its retatrutide birth control study turned away anyone who'd had another investigational drug "within the last month or 5 half-lives of this drug, whichever is longer" before screening. Five half-lives of retatrutide is about 30 days, leaving roughly 3% of the drug (halved five times).

Our read: tirzepatide's 1-month gap and Lilly's 5 half-lives rule both land at about a month for a drug with retatrutide's half-life. No regulator has confirmed that for retatrutide, so take the number to your doctor as a starting point for the conversation.

One catch applies to anything bought online. In September 2026 Australia's TGA reported a vial sold as retatrutide that held no retatrutide, and held semaglutide at about 8 times the strength of approved products. If you've injected a vial from one of the sites with retatrutide for sale, only a batch-specific lab report shows what was in it. Without one, the longer semaglutide gap is the cautious assumption.

Does reta affect birth control?

Probably the pill, going by tirzepatide. Lilly has run the retatrutide study but hasn't posted what it found. Its study NCT06039826 gave retatrutide with a combined pill (ethinyl estradiol and drospirenone) to 46 postmenopausal women and finished on July 11, 2024. As of October 31, 2026, no results are posted on ClinicalTrials.gov.

The tirzepatide numbers show why it matters. After a first 5 mg dose, the peak level of ethinyl estradiol from a combined pill fell by 59% and total exposure by 20%, and the peak arrived 2.5 to 4.5 hours late, according to the Zepbound label. The cause is slower stomach emptying, which is strongest after the first dose and fades over time. So the label asks people on the pill to switch to a non-oral method, or add a barrier method such as condoms, for 4 weeks after starting and for 4 weeks after each dose increase. The label expects hormonal methods that aren't taken by mouth to be unaffected. The UK's MHRA gives the same advice for Mounjaro.

Retatrutide's trials stepped the dose up every 4 weeks from 2 mg, so that rule adds up quickly. Here's our arithmetic, applying tirzepatide's rule to the dose steps the trials used. Treat it as a way to size the question; no retatrutide label says this.

Vomiting is the second problem. In TRIUMPH-1, about 1 in 4 people on 12 mg (25.3%) had vomiting, against 4.8% on placebo, per Lilly's topline release. The NHS says that if you're sick within 3 hours of a combined pill, take another straight away. If you have diarrhea for more than 24 hours, use condoms until 7 days after it stops; the diarrhea guide has the details. The nausea page covers the stomach numbers by dose.

Does reta affect fertility, or can it make you infertile?

Nothing points to infertility. No published retatrutide trial has reported on ovulation, sperm or time to pregnancy, so the honest answer is that it hasn't been measured. Tirzepatide's label reports no effect on mating, fertility or conception in its reproduction testing, which was done in animals, not people. Females there had fewer embryos implant and shifts in cycle timing, and the label puts both down to eating less and losing weight.

Weight loss may push fertility the other way. The NHS says trouble getting pregnant with polycystic ovary syndrome, which it now calls polyendocrine metabolic ovarian syndrome (PMOS), is usually because the ovaries don't release an egg each month. It lists weight loss medicines, for people who are overweight, among the treatments. If weight loss restarts ovulation, that could happen in the same weeks a pill may be absorbed less well.

Our read: on this evidence, the nearer risk on retatrutide is getting pregnant sooner than planned, which makes the contraception section above more urgent than any fertility worry.

For men, there's no retatrutide data on sperm or hormones, and tirzepatide's animal testing found no change in sperm shape. For the broader picture, see retatrutide for women.

Can reta delay your period?

No retatrutide trial has reported changes in periods, and the side effect lists in Lilly's Phase 3 releases don't include them. We found no published count of how often it happens, so user reports are the only signal and they can't tell you a rate.

The NHS list of common causes for a late or missed period reads like the first months on a strong weight-loss drug: pregnancy, stress, sudden weight loss, being overweight, too much exercise, and hormonal contraception. It also lists perimenopause, covered on our retatrutide and menopause page.

So take a pregnancy test first, especially if you rely on the pill and are in a dose-increase month. The NHS says to see a GP if you miss 3 periods in a row, or if a missed period comes with other changes such as weight loss, tiredness or hair growth on your face. Other side effects women report are on the retatrutide side effects in women page.

Can you take reta while breastfeeding?

Nobody has measured retatrutide in breast milk, and the Phase 2 obesity trial kept breastfeeding women out. The UK's MHRA says GLP-1 medicines should not be taken by people who are breastfeeding, because there isn't enough safety data to know whether they could harm the baby.

Of the labels here, only tirzepatide's gives measured milk levels. In a single-dose study of 11 women given 5 mg, the drug was undetectable in 164 of 171 milk samples, and the total that did show up over 28 days was under 0.02% of the mother's dose, per the Zepbound label. The same label says there's no data on effects on the baby or on milk supply. The Wegovy label has no milk data for semaglutide injections, and says not to breastfeed while taking Wegovy tablets.

The first months after birth combine the two situations with the least data: a recent pregnancy and a baby who may be feeding. Shedding hair a few months after birth can happen on its own, so it isn't automatically a drug effect (the hair loss page lists childbirth among the triggers). If you're weighing retatrutide after weaning, the dosage schedule shows what the trials used.

What to do if you get pregnant while taking retatrutide

1. Stop your injections. The Zepbound and Wegovy labels both say to stop when a pregnancy is recognized.
2. Call your doctor or midwife and tell them what you took, where it came from, your doses, and the date of your last injection. Keep the vial and any batch paperwork.
3. If you're in a Lilly clinical trial, call your study site the same day.
4. Ask whether the exposure changes your pregnancy care, and about blood sugar if you have diabetes. Tirzepatide and semaglutide have pregnancy registries; with no retatrutide label, there's no registry to point you to.

Lilly last said, on September 29, 2026, that it plans to submit retatrutide to the FDA in the first quarter of 2027 as a Biologics License Application (BLA). On October 2, 2026, the FDA decided that retatrutide is a drug, not a biological product, so an application would need to be filed under section 505 of the Federal Food, Drug, and Cosmetic Act. Lilly's appeal on that question is pending in the Seventh Circuit, and we found no ruling as of October 31, 2026 (see FDA approval). Until a retatrutide label exists, tirzepatide's is the nearest guide, and the posted results of study NCT06039826 are the piece most worth watching for.