What Causes Memory Loss And Sudden Loss Of Weight After Having Cannabis?

Hi my 20 yrs old son is a university student living away from home some time come home over weekend but most of the time doesn t want to come home last few months ago I found out he is taking cannabis n his progress in exams were very poor he s always argue with me shouting n very rude. Forgets things n losing weight also I m very stressful and worried about him plz tell me how to deal with this problem I m diabetic also I need to be relaxed but in this situation how can I he is my only son I have one daughter older than him.my husband working abroad