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What is cannabis-induced psychosis? The condition behind ‘insanity’ murder case

Diego Costa Silva began smoking cannabis aged 16 and from the age of 20 would smoke daily, the trial heard

The trial of Diego Costa Silva (right) heard that he had come to believe that his wife Fabiole Camara De Campos (left) was possessed by a serpent, and that she was going to kill him. Photograph: Facebook

Fiachra Gallagher
Eoin Reynolds
Sat Mar 9 2024 - 08:00

Diego Costa Silva killed his wife while in a state of cannabis-induced psychosis at their home in Finglas, Dublin on November 4th, 2021.

On Friday, a jury found him not guilty of Fabiola De Campos Silva’s murder, by reason of insanity. During the trial, two forensic consultant psychiatrists gave evidence that he was suffering from cannabis-induced psychosis with symptoms including paranoia, delusions and auditory hallucinations.

Dr Mark Joynt told the court that due to his mental disorder, Mr Costa Silva (35) did not know the nature and quality of his actions, did not know that what he was doing was wrong and was unable to refrain from his action.

Psychosis can be described as someone “losing touch with reality”, according to Prof Des Crowley, assistant director of substance misuse at the Irish College of General Practitioners, speaking generally about the condition.

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“It can be in the form of a delusion – a patient or person misinterprets reality,” Prof Crowley says. “For example, they think that the television is talking to them, or people are talking about them.”

Psychosis can also trigger hallucinations – sufferers might hear voices, or see things that are not there.

“That’s often when people can be told to hurt themselves or to hurt other people,” Prof Crowley says.

Mr Costa Silva’s trial heard that he had come to believe that his wife was possessed by a serpent, and that she was going to kill him.

Psychosis that is cannabis-induced is usually linked to heavy, long-term use of the drug, Prof Crowley says. Those with brain injuries or with a family history of mental disorders are at a greater risk of developing this form of psychosis, while using other drugs can also increase susceptibility.

Mr Costa Silva told Dr Joynt he had begun smoking cannabis aged 16 and from the age of 20 would smoke daily. There was also a history of bipolar disorder in Mr Costa Silva’s family, his trial heard.

Psychosis that is caused by cannabis can – and often does – extend beyond the period of intoxication, Prof Crowley said. “The presentation of the psychotic episode can actually present over a longer period of time.”

If a patient has not returned fully to their normal state after a month or so, Prof Crowley says, a diagnosis of a longer-term mental illness – like schizophrenia – should be considered.

In Mr Costa Silva’s case, he continued to display psychotic symptoms 11 days after the killing. He said that he did not think he smoked cannabis in the days immediately leading up to killing his wife.

When Dr Joynt last spoke to Mr Costa Silva in November last year, he said he found no evidence of active psychotic symptoms. He said this was one of the reasons he did not diagnose Mr Costa Silva with a more persistent illness such as schizophrenia.

Dr Joynt noted that there was a history of bipolar disorder in Mr Costa Silva’s family, placing him at a higher risk of developing a serious mental disorder – including substance induced psychosis.

Barristers for the defence and prosecution told the jury that Mr Costa Silva was not legally responsible for his actions and qualified for the special verdict of not guilty by reason of insanity under the Criminal Law (Insanity) Act 2006.

Fiachra Gallagher

Fiachra Gallagher

Fiachra Gallagher is an Irish Times journalist

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