text: ipecac, but that won't get the pot out of his system (the smoke is inhaled not ingested, DUH!) and it won't teach him a lesson; he'll just hate you and probably rebel more.  Talk with him and tell him he made a bad decision and keep a closer eye on him.  You can prevent this stuff by being around and being an influence and TALKING on a regular basis even about things unrelated to drugs.  The closer you are, the better the kid usually behaves.