Teratogenesis is a scientific term that means the development of abnormal structures in an embryo resulting in a severely deformed fetus. The word has Greek and Latin origins (Terata, meaning something that has an abnormal or unusual appearance, and genesis, meaning production). A teratogen, therefore, is a drug or chemical that causes fetal deformities. It has long been established that drugs such as Thalidomide and chemicals such as organic mercury are known teratogens. In recent years, a class of drugs known as SSRIs (selective serotonin reuptake inhibitors) has been strongly associated with malformations occurring at birth.
Zofran (ondansetron) is not literally a serotonin reuptake drug, but rather it is known as a serotonin receptor agonist. Zofran is a Carbazole derivative and, while described as a “5-HT3 agonist,” it is actually also a weak 5-HT4 antagonist. At the molecular level, it consists of two six-membered benzene rings fused on either side of a five-membered nitrogen ring.
Multiple medical and scientific studies have implicated Zofran (ondansetron) as a teratogen. In particular, Zofran has been found to significantly increase the risk of cleft lip, cleft palate, and cardiac deformities in children whose mothers took Zofran for morning sickness during the first trimester of pregnancy.
The developmental period at which an exposure occurs will determine which structures are most susceptible to the harmful effects of the drug or chemical. The first trimester of pregnancy is the period of greatest sensitivity to teratogenic insults and also is the time when most anatomic deformities are induced.