The government is lifting a 70-year-old ban on letting pilots fly while on antidepressants, citing improvements in the drugs and an unforeseen side effect of the restriction: Depressed pilots kept flying but just kept their conditions secret.

"Our concern is that they haven't necessarily been candid," Federal Aviation Administrator Randy Babbitt told reporters in a conference call.

According to Associated Press, the change in policy, which includes a degree of amnesty for pilots who lied about their diagnosis and treatment on medical certification forms, is aimed in part at clueing the government in on how many pilots suffer from a disease whose symptoms can include thoughts of suicide, FAA officials said.

The National Institute of Mental Health estimates that about 9.5 percent of people 18 and older suffer from a mood disorder. A 2009 study by Columbia University showed that as many as 10 percent of Americans were taking antidepressants. FAA officials assume the percentage is about the same among pilots.

But the agency has no hard numbers because the ban gave pilots a disincentive to report depression or treatment for it. Under the ban, airline and other pilots who suspected they were depressed but wanted or financially needed to fly generally faced a choice: seek no medication for treatment, because doing so would disqualify them, or self-medicate and lie about it on a required medical certification form — a federal crime. Neither, Babbitt said, is acceptable.

"We need to change the culture and remove the stigma associated with depression," Babbitt said. "Pilots should be able to get the medical treatment they need so they can safely perform their duties."

Under the new policy, pilots who take one of four antidepressants — Prozac, Zoloft, Celexa or Lexapro — or their generic equivalents will be allowed to fly if they have been successfully treated by those medications for a year without side effects that could pose a safety hazard in the cockpit. The antidepressants are classified as SSRIs, which help regulate mood.

The ban had endured because earlier generations of antidepressants caused concerns about side effects, such as drowsiness and seizures, Babbitt said. But a panel of medical experts for the FAA found during two years of research that newer versions don't cause side effects in everyone. When they do occur, they tend to subside in time.

In addition, the FAA will grant a sort of amnesty for pilots who have kept their treatment a secret. The agency will not take civil enforcement action against pilots who, within six months, disclose their diagnoses of depression and treatment.

Technically, the new policy would not protect pilots who lied about the issue from criminal prosecution, a spokesman for the agency said. But the inspector general of the Department of Transportation has said that prosecution would only be sought in extraordinary cases, such as when other criminal conduct was involved, according to Les Dorr, spokesman for the FAA.

Several labor unions representing aircraft owners, pilots and crews had urged the government to lift the ban, and the Air Travelers Association does not object, according to its president, David Stempler. The Army, the Civil Aviation Authority of Australia and Transport Canada already allow some pilots to fly who are using antidepressant medications.

But others say that lying on a federal form for any reason should disqualify would-be pilots.

"The FAA, by essentially granting amnesty to thousands of pilots who suffer from mental illnesses, and lied about those illnesses, is rewarding dishonesty and in so doing making our skies less safe," said Joseph Gutheinz Jr. a former commercial pilot and government investigator who teaches about aviation security and safety issues at the University of Phoenix.

A team of psychiatrists and aviation medical examiners will help the agency monitor pilots under the new policy, modeled on a program established 40 years ago to assess and treat pilots suffering from alcohol and drug abuse issues, the FAA said.