No, you should not take losartan while pregnant. Losartan carries an FDA boxed warning for fetal toxicity, the strongest safety warning the agency issues. The drug can cause serious injury and death to a developing baby, particularly when used during the second and third trimesters. If you discover you’re pregnant while taking losartan, the standard guidance is to stop the medication as soon as possible.
Why Losartan Is Dangerous During Pregnancy
Losartan belongs to a class of blood pressure medications called ARBs (angiotensin receptor blockers). These drugs work by blocking a hormone called angiotensin II, which narrows blood vessels. In adults, that’s helpful for lowering blood pressure. But in a developing baby, angiotensin II plays a critical role in kidney development, especially during the second half of pregnancy.
When losartan blocks that hormone in the fetus, the baby’s kidneys can’t function properly. Since a fetus produces amniotic fluid largely through urination, impaired kidney function leads to dangerously low amniotic fluid levels, a condition called oligohydramnios. A systematic review found that 87% of pregnancies where an ARB was used in mid-to-late pregnancy or throughout the entire pregnancy developed low amniotic fluid.
Low amniotic fluid creates a cascade of problems. The fluid normally cushions the baby and gives the lungs room to develop. Without enough of it, the fetus can develop underdeveloped lungs, abnormal skull formation, stiff joints that can’t move properly, and restricted growth overall. In some cases, low amniotic fluid leads to fetal death. It also significantly increases the likelihood of early delivery by induction or C-section.
Risks by Trimester
The timing of exposure matters. The most dangerous period is the second and third trimesters, when the baby’s kidneys are actively developing and depend on angiotensin II signaling. During this window, losartan can cause low blood pressure, kidney disease, and kidney failure in the newborn. Some infants have died from these complications.
First-trimester exposure is less well understood. It’s not yet known whether losartan increases the chance of birth defects when used only in the first trimester. Case reports have shown typical outcomes when the medication was stopped early and not continued through the rest of pregnancy. One small study of 20 pregnancies exposed to ARBs found one infant with craniosynostosis (skull bones fusing too early) and another with an inguinal hernia, but the numbers are too small to draw firm conclusions. Even in the first trimester, the rate of low amniotic fluid was 43% in a systematic review of ARB-exposed pregnancies, so the risk is not zero at any stage.
If You Took Losartan Before Realizing You Were Pregnant
Many people don’t discover a pregnancy immediately, and taking losartan for a few weeks before a positive test is not uncommon. The key step is stopping the medication as soon as pregnancy is confirmed. Case reports show that pregnancies exposed briefly in the first trimester, where the drug was then discontinued, have generally had normal outcomes. The longer the exposure continues, especially into the second trimester, the greater the risk.
Your provider will likely switch you to a pregnancy-compatible blood pressure medication and may recommend additional ultrasound monitoring to check amniotic fluid levels and fetal kidney function. If you were only exposed early, that’s reassuring, but close follow-up still helps catch any issues.
Safer Blood Pressure Medications During Pregnancy
Several blood pressure drugs have established safety profiles in pregnancy. Labetalol is generally the preferred first-line option because it works quickly, is effective, and preserves good blood flow to the uterus and placenta. Nifedipine, methyldopa, and hydralazine are also considered safe alternatives. Your provider can help determine which one fits your specific situation, including how severe your hypertension is and whether you have other health conditions.
Current guidelines from the American College of Obstetricians and Gynecologists recommend starting blood pressure medication if readings reach 140/90 mm Hg or higher during pregnancy. If you were already on losartan for chronic hypertension before becoming pregnant, you’ll still need treatment. Uncontrolled high blood pressure during pregnancy carries its own serious risks, including preeclampsia. The goal is switching to a safer drug, not stopping treatment altogether.
Planning Ahead Before Conception
If you’re currently taking losartan and thinking about becoming pregnant, the safest approach is switching medications before you conceive. Because the earliest weeks of pregnancy are when you’re least likely to know you’re pregnant, making the switch in advance removes the window of accidental exposure entirely. Talk with your provider about transitioning to labetalol or another pregnancy-safe option as part of your preconception planning, ideally before you stop using contraception.
This also applies to other drugs in the same class. All ARBs and a related group called ACE inhibitors carry the same fetal toxicity warning and are contraindicated throughout pregnancy. If you take any medication that ends in “-sartan” or “-pril,” the same guidance applies.