There’s a reason intelligence and wisdom are separate stats in D&D.

Some people just like drugs. Lots of people engage in risky behavior because they like it and are willing to take the risk. Look at basejumpers for instance.

This seems like an incredibly narrow minded view of intelligence.

Intelligence is correlated with experimentation and drug usage (and generally do-what-you-will with your body political attitudes).

Some discussion on the phenomenon here:

"We know that intelligent people have more self-control and make better decisions in general — they’re less likely to play the lottery, more likely to follow medical advice, less likely to die in accidents. As a consequence, they tend to flourish in an environment free of normative constraints. They may experiment with drugs without ever getting addicted. They may dabble in polyamory without wrecking their marriage. They may coast on their achieved identity, dismissing traditions as stifling or unnecessary."

- via: https://www.aporiamagazine.com/p/why-are-intelligent-people-...

My theory is that his drug usage started when he was studying at Stanford. He was probably taking Ritalin and then started taking other stimulants.