What medication was given to pregnant women for morning sickness that led to significant birth defects?

Thalidomide is known for its severe consequences when prescribed to pregnant women for morning sickness in the late 1950s and early 1960s. It was marketed as a sedative and antiemetic, but it was later discovered to cause significant birth defects, including phocomelia, where babies were born with severely shortened limbs, as well as a range of other physical abnormalities. The drug's teratogenic effects were catastrophic and led to a large public health crisis, resulting in stricter regulations on drug testing and approval for pregnant women.

In contrast, phenobarbital is primarily used as an anticonvulsant and has a different risk profile. Metoclopramide is typically used to treat nausea and gastroparesis but has not been associated with the same level of teratogenic effects as thalidomide. Ondansetron, another antiemetic, is often prescribed during pregnancy to manage nausea with a better safety profile compared to thalidomide. Thus, thalidomide stands out as the medication linked directly to significant birth defects in this context.