In 2000, a study was done in which 20 healthy non-depressed volunteers were given the SSRI antidepressant Zoloft (Sertraline). Two weeks into the study two volunteers became dangerously suicidal.

As reported in the Guardian on Sunday 21 May 2000

Much more info at the link

Alarming evidence from a new British study shows that the Prozac class of antidepressants can make healthy men, women and children with no history of depression feel suicidal.

The research undermines the claims of Eli Lilly, makers of Prozac, that people who kill themselves while on the tablets do so because of their depression, and that the disease, not the drug, is to blame for their suicide.

Its findings are particularly worrying because of the increasing numbers of people, including children, who are being given the drugs by their GP for mild depression, and who are not seriously clinically ill.

[...]

It found that two out of 20 healthy volunteers on an antidepressant in the Prozac class called Lustral (or Zoloft in the USA) became dangerously suicidal, compared with none of them when they were put on an antidepressant of a different class called reboxetine.

One 30-year-old woman who took part had a nightmare about having her throat slit after one week and by the end of a fortnight, was suicidal. "She felt hopeless and alone. It seemed that all she could do was to follow a thought that had been planted in her brain from some alien force. She suddenly decided she should go and throw herself in front of a car, that this was the only answer.

"It was as if there was nothing out there apart from the car, which she was going to throw herself under. She didn't think of her partner or child," says the study, published in the journal Primary Care Psychiatry.

Later she completed a diary entry, describing herself as jumpy, anxious and suspicious. "Her mind was racing and spiraling out of control. Then it went blank except for the clear thought that she must kill herself violently by throwing herself beneath a car or a train."