Shane Clancy's mother Leonie with Professor David Healy

THE family of a young man who carried out a murder-suicide 11 months ago is to take a legal action against the pharmaceutical company that produces the anti-depressant medication he was taking, as they believe the drug drove him to carry out his crime.

The Sunday Tribune understands that Shane Clancy's family is "determined" to sue pharmaceutical company Lundbeck. The family has not yet filed the lawsuit but plans to do so imminently to raise awareness about potential side-effects they believe anti-depressants can have on users. They have not ruled out taking a class action, which would involve several families taking a joint action.

At an inquest into Clancy's death, professor David Healy from the University of Cardiff said that in a small number of cases anti-depressants can cause people to become potentially homicidal or suicidal. Healy also said he believed that the 22-year-old had suffered an adverse reaction to the drug. He stressed that many people can use the drug safely, but said he had concerns over the safety warnings given to the drug in Ireland. Clancy's mother, Leonie Fennell, has spoken about her belief that her son's depression was made worse and caused him to carry out his crime.

A spokeswoman for Lundbeck declined to comment but pointed to its statement released after the inquest in April: "It was stated at the inquest that citalopram may have caused the behaviour and actions of Shane Clancy that resulted in his self-inflicted death, that of Sebastian Creane and the wounding of two other people. Extensive scientific studies have shown that there is no evidence linking citalopram to violent behaviour. There are trials which show that citalopram has the potential to reduce, rather than provoke, irritability, aggression and violent behaviour."

The Trinity College student stabbed Sebastian Creane at his home in Bray before turning the knife on himself on 16 August last. He also stabbed his former girlfriend Jennifer Hannigan and Creane's older brother Dylan in the attack. Both have recovered. The 22-year-old had become depressed over the break-up of his relationship with Hannigan a few months earlier.

One week before the incident, Clancy overdosed on anti-depressants in a suicide attempt and was later given another prescription for more. When he carried out his attack he had "toxic to fatal" levels of antidepressants in his system.