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By Lisa Richwine

WASHINGTON (Reuters) - A U.S. government medical reviewer who raised concerns about antidepressant use by children said on Thursday he was pressured to hide information and submit an altered document to congressional investigators.

Dr. Andrew Mosholder, a Food and Drug Administration epidemiologist, said agency officials did not want lawmakers to know the agency was conducting an internal probe of whether he leaked his concerns about antidepressant risks to a reporter.

Mosholder concluded last year that children and teens who took antidepressants during clinical trials were more likely to report suicidal thoughts or actions. His superiors disagreed and prevented him from presenting his findings at a public meeting last February.

The Senate Finance Committee began investigating how regulators were handling the concerns about the drug's use. Mosholder wanted to give the panel an affidavit drawn up for the FDA probe in which he said he did not leak the information.

In testimony before the House Energy and Commerce Committee on Thursday, Mosholder said FDA officials told him to remove a reference to the agency's probe, as well as some names to protect privacy.

"Had Dr. Mosholder not acted to thwart the submission of an altered document to a bona fide congressional investigation, a criminal act of obstruction of justice would have occurred," charged Rep. Peter Deutsch, a Florida Democrat.

Mosholder said FDA officials told him not to tell congressional investigators the document had been changed.

In a May 4 e-mail to Mosholder, which was read at the House Committee hearing, an official in the FDA chief counsel's office wrote, "I don't think that it's necessary to indicate that this document represents a version of the earlier one by noting things have been omitted. That simply invites the committee to ask further questions about what was in the earlier version."

Mosholder said that made him uncomfortable and he gave the committee his original document minus the names.

FDA spokesman Jason Brodsky said the agency does not disclose the existence of internal probes because of a need "to protect the integrity of the investigation."

The FDA has been accused of trying to conceal information throughout the antidepressant controversy. Despite Mosholder's findings months ago, top officials did not confirm a link between antidepressants and suicidal behavior in youth until last week.

Dr. Robert Temple, director of the FDA's Office of Medical Policy, defended the agency's actions. He said data were unclear and officials wanted to be certain of the risks before warning doctors and the public.

"We thought it was very important to get the right answer," Temple said at the hearing.

For some patients, the drugs can be life-saving by relieving depression, a serious mental illness that itself raises the risk of suicide.

As early as 1996, one FDA reviewer questioned if Pfizer Inc.'s Zoloft might raise the risk of suicidal behavior in children. FDA officials told lawmakers they fully investigated but found no evidence of a problem.

The FDA probably will take a panel's advice to highlight the chances of suicidal thoughts and actions among youth in a "black box" on antidepressant labels, Temple said. Another option is a warning in bold letters, without the box.

A decision is likely within weeks, Temple said.

An FDA analysis estimated 2 percent to 3 percent of children and teens who take antidepressants might have an elevated risk for suicidal behavior. But no suicides occurred in studies of more than 4,000 children.

Antidepressants include Eli Lilly and Co.'s Prozac, Pfizer's Zoloft, GlaxoSmithKline Plc's Paxil, Forest Laboratories Inc.'s Celexa and Wyeth's Effexor. Prozac also is sold under the generic name fluoxetine.