Anybody who has done Meth before. Maybe you can help?

Ok, so my friend recently got out of rehab for doing meth. He has “supposedly” been clean, except for the “slip up” a couple of nights ago. Well, last night and the night before has been coming home saying that he is still coming down off of his high. How many days does it take to come down off of one time using meth? What are other major ways to tell if he has recently used?

Thanks so much! Any help you can give me is extremely appriciated.