ok... this is the convo i would have...
"hey son, some buds of mine and a nice pill i had stashed , well, i am not sure if i used them, or if , in fact , you may have found them, and used them, and anyway, it got me thinking that, hey, i have never really had this adult chat with you, about my using drugs... obviously i do, and well, you are an adult now, and i want you to know i am
cool with you wanting to experiment with drugs. so, whether you took them or not, doesnt matter at all. because i am sorry, that i didnt offer you to share some
times with me, and in fact, because i had never had this convo, you felt like you had to pinch them from me, if it was you, so any way son, i am sorry i havent
recognised your maturity and adult hood... so, if you want some pills or grass, maybe we can get some, and share .... responsibly, in moderation. that way, if my
stash seems like it is a little depleted, then i know for sure, that it is just my bad memory, and not you, and because, we have no need to steal from each other, because that just isnt on, instaed we can just ask each other. let me know if you find some nice acid some time." etc etc
ok, so i know that rambled.
but, this is a possible tact to take, and in fact would be how i approach the matter.
kids like to be trusted with the knowledge of what their parents do. esp with drugs.
a 20 year old is old enough to take drugs, and old enough to be trusted with the knowledge of parents use. and old enough to share drugs with. in moderation. best that they learn how to use drugs in moderation with you, than learn how to be irresponsible without you. now i am not saying that this will in fact save them from any acts of irresponsibilty, not at all. we all know that irresponsible drug use happens sometimes, and that those times are good lessons to learn. but, at least you will have taught him a mode of responsibilty, whereas some kids never get taught that and only learn irresponsibilty. you will also have taught him an adult mode of
communication, and trust.
it is this openess and trust that i feel is important. for it may be a possibilty that had this convo been had two years before or more, and it was in the open, than it would have been impossible for him to pinch some stash, and get away with it, with the chance that it would never be talked about.
there can only be positive things come from openess and trust.
good luck.