This is a serious concern to be addressed with great care. It is also important that the boy does not stay away in a hostel. There is no way to test how many days back one has taken drugs. Other than the patient has taken it within the last couple of days it will not show up in the blood stream. Instead of a psychologist
the boy needs love and care at home. If the situation seems worse then u need to get him to a Rehab where he would be monitored. Please be careful in choosing a Rehab facility as most of them are commercial.