I'd call his parents TODAY and have an honest compassionate direct conversation, sparing no detail of the severity.
As the mother of a son who became a heroin addict his 1st semester of college, I would have apprec. that phone call. Sometimes we do need to take action. You don't know the outcome of your convers. with the parents but you do know the outcome of the progression of addiction. Bless you for being concerned and proactive.