About 15 percent of women in the United States suffer from anxiety disorders and depression during their pregnancies, and many are prescribed antidepressants. However little is known about how early exposure to these medications might affect their offspring as they mature into adults. The answer to that question is vital, as 5 percent of all babies born in the U.S. -- more than 200,000 a year -- are exposed to antidepressants during gestation via transmission from their mothers.

Now, a UCLA team has studied early developmental exposure to two different antidepressants, Prozac and Lexapro, in a mouse model that mimics human third trimester medication exposure. They found that, although these serotonin-selective reuptake inhibiting antidepressants (SSRIs) were thought to work the same way, they did not produce the same long-term changes in anxiety behavior in the adult mice.

The mice exposed to Lexapro had permanent changes in serotonin neurotransmission and were less anxious as adults than the mice exposed to Prozac, said study senior author Anne M. Andrews, professor of psychiatry and chemistry and biochemistry and the Richard Metzner Endowed Chair in Clinical Neuropharmacology at the Semel Institute for Neuroscience & Human Behavior and California NanoSystems Institute.

"This was quite surprising, since these medications belong to the same drug class and are believed to work by the same mechanism. The implications of these findings are that with additional investigation, it may be possible to identify specific antidepressants that are safer for pregnant women," Andrews said. "It's important to recognize that major depressive disorders and anxiety disorders are serious medical conditions that often require therapeutic intervention. Prescribing the safest medication for mother and child is paramount."

The results of the six-year study appear early online Dec. 19, 2014 in the peer-reviewed journal Neuropsychopharmacology.