Jack Lindsay died in 2012 at age 17 when he took several medicines which proved toxic because he was epileptic.
Along with his epilepsy Mr Lindsay suffered from autistic spectrum disorder, had mental health problems and frequently drank alcohol and smoked cannabis.
He was violent at school and had committed a sexual crime by the time he was 15.
Mr Lindsay was periodically under the care of Child Youth and Family but the agency was forced to step back because the law prevented it holding people in its care after their 17th birthday.
Hi death was not linked to any lack of support, but in his report Coroner Ian Smith, still raised concerns that young people like him struggle to cope when they lose the full support of CYFS.
"In Jack's case, there was some continuance [of support from CYF]. It is, however, my view that that is not enough. I have stated previously that 17 is far to young to cut these young people adrift" Mr Smith wrote.
Ian Smith recommended in, at least, two other reports into the deaths of teenagers that the government change the law so full Child Youth and Family support can be extended to over 17s.
Chief Coroner Neil Maclean said Mr Smith was not alone among coroners in his concern.
"We often see a case where good support - be it coaxing them into education, drug education, heath programmes, wellness programmes that sort of thing - are chugging along quite satisfactorily and then suddenly bang, it stops.
"Somehow we expect the young person to to go cold turkey and somehow magically sort it out themselves," Judge Maclean said.
Social Development Minister, Anne Tolley said the Government did not plan to change the law so CYFS could extend full care to over 17s.
"All young people leaving CYF care are enrolled with Youth Services when they are not in education, training or work which provides them with wrap-around social service support including accommodation and money management assistance" Ms Tolley said in a statement provided to Radio New Zealand.
Ministry of Social Development said it was already working with other agencies to strengthen the support it gives to people moving from state care to full independence.