I'm sure everyone on here knows this already, but Carl Sagan was secretly (the Mr. X essays) an advocate for marijuana use. I myself earned a BS in Mathematics while getting high pretty much every day I wasn't studying or being tested (it definitely interferes with your ability to do maths while you're stoned, but outside of that, nope).
It's a drug that anyone can use with a significant positive effect to their life as long as they are possessed of the most moderate amounts of self-actualization and self-control (I say this as the sire of two bloodlines extremely predisposed to addiction).
Since NDGT is a minority, there's a chance that he has never used weed (since the war on drugs is plainly a war on minorities), but I'm fairly certain that someone as worldly as he (and as influenced by Dr. Sagan) has at least experimented with the drug. And he may not admit it publicly, but read the Mr. X essays. That's one of our greatest minds.