Subsequent anxiety-related behavior in rats exposed to low-dose methadone during gestation, lactation or both periods consecutively

► Gestational or lactational methadone exposure did not affect physical development. ► Lactational methadone alone increased activity and possibly anxiety. ► Gestational plus lactational methadone decreased activity but increased anxiety. ► Some effects were specific to sex and age. ► Overall the methadone effects suggested increased anxiety.