By "weed" do you mean marijuana? I don't think that's in any of their writings. As far as smoking tobacco goes, it was not generally known to be harmful when Lewis was alive - many, many Christians smoked (and still do). As for alcohol, as long as it's taken in moderation, it's a perfectly acceptable biblical practice. You might want to try out these verses on your friends:
John 2:1-11 On the third day a wedding took place at Cana in Galilee. Jesus' mother was there, and Jesus and his disciples had also been invited to the wedding. When the wine was gone, Jesus' mother said to him, "They have no more wine." "Dear woman, why do you involve me?" Jesus replied, "My time has not yet come." His mother said to the servants, "Do whatever he tells you." Nearby stood six stone water jars, the kind used by the Jews for ceremonial washing, each holding from twenty to thirty gallons. Jesus said to the servants, "Fill the jars with water"; so they filled them to the brim. Then he told them, "Now draw some out and take it to the master of the banquet." They did so, and the master of the banquet tasted the water that had been turned into wine. He did not realize where it had come from, though the servants who had drawn the water knew. Then he called the bridegroom aside and said, "Everyone brings out the choice wine first and then the cheaper wine after the guests have had too much to drink; but you have saved the best till now." This, the first of his miraculous signs, Jesus performed in Cana of Galilee. He thus revealed his glory, and his disciples put their faith in him.
1 Timothy 5:23 Stop drinking only water, and use a little wine because of your stomach and your frequent illnesses.
