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The mother of a man who murdered his ex girlfriend's new boyfriend before killing himself believes antidepressants drove him to kill the young man.

Leonie Fennell's son Shane Clancy, 22, stabbed his ex girlfriend Jennifer Halligan's boyfriend Sebastian Creane to death in Bray in 2009 and had been prescribed the antidepressant drug SSRI (Selective Serotonin Reuptake Inhibitors) Citalopram 17 days before his death.

His heartbroken mother now believes that Shane would never have killed Mr Creane and himself had it not been for the antidepressants he was prescribed, as she issued a heartfelt plea to the Irish public to use antidepressants 'with caution'.

In a frank account in the Irish Independent, Ms Fennell wrote: "In 2009, my son killed his ex-girlfriend's new boyfriend by stabbing him once. He then killed himself by stabbing himself 19 times; he was 22.

"We could not comprehend how Shane could harm himself, never mind another person.

"The ridiculousness of the life we are left with never ceases to shock me. Shane was a very kind person; he liked to help others and never took drugs or alcohol.

"How could our family be left in this situation? It seemed just like a bad dream, an everlasting nightmare."

Ms Fennell goes on to explain that the incident came as a 'bolt out of the blue' and the family 'lived/existed for a long time in severe shock'.

But after reading an article by Dr Michael Corry which stated that Shane "would not have done what he did, had he not been on antidepressants", Ms Fennell arranged to meet the doctor.

She said what followed was "the start of a journey of discovery" and that Shane did not have a mental illness, "undiagnosed or otherwise".

Psychopharmacologist Dr David Healy believes Shane would not have done what he did without the antidepressants.

He said: "In my opinion, it is almost inconceivable that Shane would have done what he did had he not been on the antidepressant," the Irish Independent reports.

He added: "There is clear evidence that drugs like Citalopram can cause outcomes like this and very clear evidence that rather than coincidentally being on the drug, Shane was affected by the drug in a way that clinches it that the drug caused the problem."

Ms Fennell is working to spread awareness of this belief and concluded with a passionate statement: "It is my honest opinion that mainstream psychiatry and, on occasions, your friendly GP are causing more harm than good by clinging to the medical model mantra.

"We can only hope that Shane's experience will caution others that these drugs are far from harmless.

"I did not sign up for this and yet, I am not the victim here - my son and the young man he killed are the actual victims."