How long does meth stay in the human body and how can I tell if my son is using?

A co-worker of mine has told me she knows her son is using meth and she doesnt know how to go about confronting. She wants to help him ,but she has no info on it. She asked me about it ,I told her I have used it, some years past and told her its an awful spiral down to ruin. She would like to know how long it stays in the system and any other useful infor mation she can get.Thank you for your help.

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