The author of 15 books on the history of medicine, Dr. Healy has testified against some of the major drug companies in the trials of families suing after a relative has committed a violent act while taking an antidepressant. In several trials, he has helped families win large judgments or settlements, lawyers say.

Dr. Healy's assertions have prompted strong criticism from some in the pharmaceuticals industry who say his studies misinterpret or distort data. And his credentials as an expert witness have come under question at times. In a 2002 trial against Pfizer Inc., maker of the antidepressant Zoloft, a U.S. district court judge in Kansas disqualified Dr. Healy's testimony, saying there were "glaring, overwhelming and unexplained" flaws in his analyses of Zoloft's side effects.

(In 1999, Dr. Healy tested Zoloft on 20 healthy volunteers at his university in Wales and found that two expressed thoughts of killing themselves. He published the results in two peer-reviewed medical journals, Primary Care Psychiatry and Psychological Medicine.)

The Kansas judge then dismissed the case.

"Whenever he uses [Zoloft] data we are able to show that he has literally falsely represented those data ... or grossly misinterpreted them," says Malcolm Wheeler, a lawyer at Wheeler, Trigg, Kennedy LLP, a Denver law firm, who represented Pfizer in the Kansas trial. Dr. Healy denies that assertion.

Attacking Dr. Healy on another front, Eli Lilly & Co., the maker of Prozac, said in a statement: "Healy has been and continues to be a paid witness for trial lawyers in lawsuits filed against companies that market antidepressants. As such Healy may have a vested interest in discrediting those products."

Dr. Healy denies any such bias. He says he has testified for plaintiffs in about a half-dozen trials since 1997, earning at most $20,000 as a witness in some years. He says that 120 different groups of plaintiffs have asked him to testify but that he turned down the vast majority because the cases lacked sufficient evidence. He also notes that he earns about $10,000 a year consulting for various drug companies (none of them antidepressant makers). All of his funding comes from his university salary, drug companies, and trial testimony, he says.

Dr. Healy began charting the side effects of SSRIs while doing postgraduate research at Cambridge University in the late 1980s. One of the first patients he put on Prozac wound up feeling reckless and suicidal, he says. Soon after, Dr. Healy moved to the University of North Wales, where another patient he treated with Prozac tried unsuccessfully to drown himself. Convinced that his patients' reactions were drug-induced, Dr. Healy published his findings in the medical journal Human Psychopharmacology.

"More than 50 million people world-wide have taken Prozac since it first came on the market ... and it has significantly improved millions of lives," says Tarra Ryker, a spokeswoman for Lilly.

As Dr. Healy continued his campaign, a handful of American researchers also were writing to medical journals with similar concerns. By the mid 1990s, dozens of families had filed lawsuits against antidepressant makers accusing the drugs of driving their loved ones to violence.

In 1997, a California law firm asked Dr. Healy to testify in a suit filed by the children of William Forsyth, a Hawaii resident in his 60s who fatally stabbed his wife and killed himself with a kitchen knife 10 days after starting to take Prozac. Pointing to the absence of violent behavior in Mr. Forsyth's past, Dr. Healy testified that Prozac appeared to have caused the man's actions. The jury, unconvinced, ruled in Lilly's favor, but the case put Dr. Healy's name in circulation among trial lawyers as a witness for bereaved families and an opponent of antidepressant makers.

In 2001, Dr. Healy's testimony was enlisted in a case in U.S. district court in Wyoming concerning a man who fatally shot three family members and himself after taking Paxil for two days in February 1998. In this case, plaintiffs, led by the man's son-in-law, won an $8 million verdict against SmithKline Beecham, a company that now is part of Glaxo.

The issue gained much wider public attention in Britain -- and ultimately in the U.S. -- after Dr. Healy appeared in two influential BBC documentaries, in 2002 and 2003, that questioned the safety of Paxil. It was during this period that Dr. Healy obtained the internal GlaxoSmithKline memo that figures in Mr. Spitzer's lawsuit.

The Spitzer team learned of the memo after Dr. Healy distributed a copy at a press conference about antidepressant side effects in Bethesda, Md., this past February. Written in October 1998, the memo states it would be "commercially unacceptable" to publish data indicating poor results in treating children with Paxil.

From his analysis of various data, Dr. Healy has concluded that SSRIs cause an extra one suicide per thousand people participating in clinical trials for depression. Estimating that about two million Americans are taking SSRIs for clinical depression, he figures that these SSRIs could be causing up to 2,000 suicides a year in the U.S. -- deaths he believes could be prevented if SSRIs carried better warnings.

In vigorously pressing his case, Dr. Healy has sometimes worked against his own best interests. For example, in a speech at the University of Toronto, he showed a slide of British serial killer Harold Shipman -- a doctor who killed his own patients by giving them lethal injections of painkillers -- to make the point that patients who put their trust in the medical profession are sometimes abused. Soon after, the university rescinded a job it had offered him at its Center for Addiction and Mental Health, saying in a letter to Dr. Healy that it was alarmed by the "extremity" of his views and the "scientifically irresponsible" accusations he had made against antidepressants.

Despite the controversy, Dr. Healy's efforts have spurred public debate that contributed to British medical authorities' decision last year to ban the use of Paxil in children. Thanks in part to his lobbying, the British also are attempting to better track patients' experiences with drug side effects. "He's a man with a certain point of view and he puts it very forcefully," says Alasdair Breckenridge, chairman of the Medicines and Healthcare Products Regulatory Agency, Britain's equivalent of the Food and Drug Administration.

Write to Jeanne Whalen at jeanne.whalen@wsj.com¹