Incidentally, it's been pretty well documented that GR didn't just experiment with illegal drugs. He started smoking pot seriously during STAR TREK's third season if not sooner, and later got addicted to cocaine. Can't say I admire that behavior.
Not refuting it, but could you tell me where that information comes from? It wouldn't surprise me that he got into drugs along with the whole sweep of the counter-culture movement, and I read that he married Majel Barrett in a Buddhist-Shinto ceremony while kind of implies him getting into eastern ideas ala the Beatles, but this is the first I've heard of him being addicted to coke.
Of course, I didn't know about Nimoy's bout with alcoholism until fairly recently.
I got Roddenberry's marijuana consumption from INSIDE STAR TREK by Justman and Solow (recommended). That book might have mentioned his cocaine addiction as well; I read a borrowed copy and have since returned it. I'm sure I've seen his cocaine problem mentioned in various TNG-era contexts. It was a somewhat debilitating predescessor to his very debilitating end of life health problems that eventually put him in a wheelchair.
I too learned (relatively) recently about Leonard's drinking problem. He says he was an alcoholic by the third season, as this misleading photograph clearly illustrates, but you have to hand it to him: it never showed in Spock.