A young man found drowned in the Thames had suffered from substance-induced psychosis after smoking cannabis heavily.

The Gazette put out an appeal in February after Borex Tatsa, 18, went missing from his home near Forest Road, Haggerston, on February 7. But his body was discovered three weeks later on February 28 in the water near to Rotherhithe.

At an inquest into his death, Poplar Coroner’s Court heard how Cameroon-born Mr Tatsa had been referred for urgent psychiatric assessment last June, after he had been “withdrawn, behaving strangely and talking to himself”.

He was diagnosed with substance induced psychosis, sectioned under the Mental Health Act, and prescribed anti-psychotic drug Respiradone.

In a statement read out in court, Dr Charlotte Johnston-Webber, consultant psychiatrist at the East London NHS Foundation Trust explained that Mr Tatsa had been smoking cannabis heavily for a number of years, which is a significant risk factor for the development of a psychotic illness.

She added: “The stress of a stabbing he experienced in early 2014 in addition to his substance misuse seems to have precipitated the onset of his illness. On coming to the UK he had become involved with local gangs, and was probably quite vulnerable to exploitation. I also suspect that there are other social stresses related to gang involvement of which we are not aware.”

She continued: “He made good recovery and although his compliance with medication was doubtful at the time of his death, there doesn’t seem to be any indication he was becoming unwell again. His death at such a young age is a tragedy.”

His mother wept as Coroner William Dolman recorded an open verdict.

He said: “We don’t know how long he had been in the water but the evidence suggests more than a few hours and possibly several days.

“We don’t know what compelled him to enter the water, there was no evidence to suggest that he was suicidal at the time. How did he get into the water, did he trip, did he fall, did he move deliberately into the water from the shore? It’s unknown, was any third party involved? There are a lot of gaps.

“One thing we do know is the effect of drugs on his mental health, which was grave.”