If you are planning a pregnancy, the stopping window is counted in months rather than days — and it differs by medicine and by which regulator's document you read. Semaglutide: at least two months before a planned pregnancy, in the US prescribing information and the European summary of product characteristics alike. Tirzepatide: at least one month in the European document, and no pre-conception window at all in the current US one. This article covers those instructions and where each comes from, the contraceptive interaction the two jurisdictions read in opposite directions, and where the pregnancy-outcome studies disagree.
Washout: the gap between a last dose and a planned conception, set so the medicine has cleared. GLP-1 medication has a long half-life, which is why the gap is counted in months.
How long before trying to conceive should you stop?
Semaglutide is two months, tirzepatide is one month in Europe and unspecified in the United States.
Both the US prescribing information and the EU summary of product characteristics instruct discontinuing semaglutide at least two months before a planned pregnancy, citing the long half-life. For tirzepatide, the EU document instructs at least one month, while the current US document says only to discontinue when a pregnancy is recognised and gives no pre-conception window (product information). Semaglutide's two-month figure does not transfer to tirzepatide.
The European documents say more than the washout sentence. For semaglutide, the EU SmPC states it should not be used during pregnancy at all, and should be discontinued if a patient wishes to become pregnant or if pregnancy occurs (EU SmPC). For tirzepatide, it goes a step earlier: not recommended during pregnancy, and not recommended in women of childbearing potential who are not using contraception (EU SmPC).
Singapore's own section 4.6 is not published on the public formulary portal, so each instruction above is attributed to the document it comes from.
Oral contraceptives and tirzepatide: the same data, opposite instructions
The US and EU report near-identical pharmacokinetics and then tell patients to do different things.
The US prescribing information advises patients using oral hormonal contraceptives to switch to a non-oral method, or add a barrier method, for four weeks after starting tirzepatide and four weeks after each dose increase. Its stated mechanism is delayed gastric emptying, largest after the first dose (US label).
The EU summary of product characteristics reports the underlying numbers. After a single 5 mg tirzepatide dose alongside a combined oral contraceptive, peak concentrations fell by 59% for ethinyl estradiol, 55% for norelgestromin and 66% for norgestimate. The SmPC then concludes that this reduction is not considered clinically relevant and that no dose adjustment of oral contraceptives is required (EU SmPC).
One qualification: the EU conclusion is stated for a single dose, while the US advice targets initiation and each escalation.
For semaglutide the European document is simpler. Exposure to ethinylestradiol was unaffected, levonorgestrel exposure rose about 20%, and the SmPC concludes that semaglutide is not anticipated to decrease the effectiveness of oral contraceptives (EU SmPC).
If you take an oral contraceptive, say so at your consultation. Which instruction applies to you is a clinical decision.
What is known about fertility itself
The human effect is not established, and what the evidence does show is that weight loss improves reproductive function whatever produced it.
The EU document for semaglutide states plainly that the effect on fertility in humans is unknown. In rat studies, male fertility was unaffected, while female rats showed an increase in oestrous cycle length and a small reduction in the number of ovulations at doses associated with maternal weight loss (EU SmPC). "Unknown" and "no effect" are different statements.
A 2025 narrative review reaches a similar conclusion in humans: reproductive function improves after weight loss achieved with or without these medicines, and whether they add a direct benefit beyond it remains unclear. The same review warns that weight loss during pregnancy is associated with adverse fetal outcomes (Couldwell 2025).
Fertility can improve during treatment, and treatment is the thing to stop before conceiving — which makes contraception a live question rather than an afterthought.
Where the pregnancy-outcome studies disagree
They disagree on the direction of effect, and that disagreement is the current state of the evidence.
Three database studies published within a year of each other reached different conclusions. A US TriNetX cohort matching 4,267 people per arm found preconception GLP-1 use associated with lower rates of gestational diabetes, hypertensive disorders of pregnancy, preterm delivery and caesarean delivery (Imbroane 2025). A single-institution cohort of 448 exposed against 1,344 unexposed found higher rates of preterm delivery (17% versus 13%), gestational diabetes (20% versus 15%) and hypertensive disorders (46% versus 36%) (Maya 2025). A US Truveta cohort also found higher risks — and the same elevated pattern in people who had stopped before pregnancy as in those exposed during it, which led its authors to attribute the excess to rebound after discontinuation rather than fetal exposure (Yu 2026).
A systematic review of 36 studies found no consistent association with major congenital malformations, fetal growth restriction, stillbirth or neonatal mortality, described the maternal-outcome findings as heterogeneous and not reproducible from study to study, and noted that data on continued use through gestation remain limited (Ozbek 2026). An absence of a consistent signal is weaker than a demonstration of safety.
In a Danish nationwide cohort of 756,636 singleton pregnancies, periconceptional exposure was associated with increased preterm birth where the medicine was used to treat diabetes, and not where it was used for weight management — the authors point to the underlying diabetes rather than the drug (Hviid 2026). That subgroup is small, so this is a lead, not a settled answer. Several of that study's authors disclose funding or consulting ties to the manufacturer, and it does not include tirzepatide.
Stopping with a plan, not abruptly
In a TriNetX cohort, preconception GLP-1 use was associated with a gestational-diabetes risk comparable to non-users — 16.3% against 16.8% — while abrupt discontinuation close to conception was associated with a 53% relative increase, which the authors attribute to steeper weight rebound (Banerjee 2026). Tirzepatide was pooled with other GLP-1 medicines there, so it gives no drug-specific figure, and the design is observational.
At GetLean, our philosophy is that the medication is the catalyst and what you keep is the result. The washout is when everything built around the medication has to hold on its own, which is an argument for raising family planning at the first consultation.
Individual results vary, and these cohort figures describe the populations studied. Timing a prescribed medicine around a planned pregnancy is a decision for you and your doctor.
Common questions
How long before pregnancy should you stop GLP-1 medication?
It depends on the medicine and the document. Semaglutide: at least two months before a planned pregnancy, in both the US and EU documents. Tirzepatide: at least one month in the EU document, with no pre-conception window in the current US one (product information). Raise family planning with your doctor.
Does GLP-1 medication stop the pill from working?
For tirzepatide the two jurisdictions disagree. The US label advises switching to a non-oral method or adding a barrier method for four weeks after starting and after each dose increase (US label); the EU SmPC reports peak-concentration drops of 55 to 66% and concludes no dose adjustment is required (EU SmPC). For semaglutide, the EU SmPC expects no reduction in effectiveness (EU SmPC).
Does GLP-1 medication affect fertility?
The human effect is stated as unknown in the EU semaglutide document; in rats, male fertility was unaffected while female rats showed a longer oestrous cycle and fewer ovulations at doses associated with weight loss (EU SmPC). Reproductive function improves after weight loss however it is achieved, and a drug-specific benefit beyond that remains unclear in humans (Couldwell 2025).
What if you become pregnant while taking it?
Tell your doctor straight away. The EU semaglutide document instructs discontinuing if pregnancy occurs, and states semaglutide should not be used during pregnancy (EU SmPC). Across 36 studies there was no consistent malformation, growth-restriction or stillbirth signal — absence of signal rather than proof of safety (Ozbek 2026).
Do the pregnancy studies agree with each other?
No. One US database cohort found lower rates of gestational diabetes, hypertensive disorders and preterm delivery after preconception use (Imbroane 2025); two others found higher rates of similar outcomes (Maya 2025, Yu 2026). The direction of maternal-outcome effects is genuinely unsettled.