Question: is this a 2) strong advice, 1) weak advice 0) no advice?

Although we know of no studies of the validity of self-reports among cannabis users in non-treatment settings, studies of alcohol (Del Boca & Darkes, 2003) and tobacco (SRNT Subcommittee on Biochemical Verification, 2002) users in these settings suggest self-report is accurate. 
user
This is no advice
assistant