In the final days of the 20th century, a North Wales psychiatrist named David Healy conducted a curious study, and with more than a curious result. Twenty volunteers with no history of psychiatric problems were recruited, half of whom were given the drug Zoloft, an antidepressant from the Prozac family of drugs known as the SSRIs, or "selective serotonin reuptake inhibitors." The other half were given an antidepressant that, unlike Zoloft and Prozac, does not selectively target the brain chemical serotonin. Each group took their respective drug for two weeks and then, shortly thereafter, switched to the other.

Healy had designed his "healthy volunteer study" to compare the psychological experience of being on a serotonin antidepressant versus a non-serotonin antidepressant, but before he knew it, two of his volunteers became dangerously agitated and suicidal. Both were taking the SSRI drug. The adverse reactions couldn't easily be blamed on psychological instability – these were healthy volunteers. And the rate of 10 percent made it clear that such results were not so rare as to be incidental.

Healy was surprised at the effect, but he would not stay surprised. Some months later, when serving as an expert witness in a civil action against Zoloft's manufacturer, Pfizer, Healy obtained access to the company archives. There he discovered an unpublished study from the 1980s in which healthy female volunteers were given either Zoloft or a placebo. The study was canceled four days later, after all those taking Zoloft began complaining of agitation and apprehension. Healy's case was not so bad; in fact, some of his volunteers rated Zoloft positively. Of the two who did not, one was a 30-year-old woman who, within two weeks of starting the drug, became obsessed with the idea that she should throw herself in front of a car. "It was as if there was nothing out there apart from the car which she was going to throw herself under," Healy reported. "She didn't think of her partner or child."

The Zoloft case was not Healy's first involvement in a civil action against an SSRI manufacturer. Earlier, he had been involved in a wrongful death suit against Eli Lilly, the maker of the much celebrated SSRI drug, Prozac. An internationally renowned psychiatrist as well as a historian of psychiatric medicine, Healy's recruitment onto the plaintiffs' side was a small but significant victory. Prior to his involvement as an expert witness, Healy had already raised a number of questions about the SSRIs, including the possibility that they might produce agitation and other problems with an unusual frequency, sometimes leading to suicide. Healy was also ideal because he's not a radical, nor an outsider; he has done research and consulting for various drug companies, and has himself prescribed SSRIs and other psychiatric drugs. In fact, he had been consulted on several SSRI suicide cases in which he had concluded that the SSRIs were not at fault.

This view changed, however, with the case of William Forsyth.