>When Ronald Graham, a concerned friend and fellow mathematician, bet him $500 that he couldn’t stay off his drug of choice for a month, Erdős accepted and easily won the challenge. When the 30 days was up, Erdős said to Graham, “You’ve showed me I’m not an addict. But I didn’t get any work done. I’d get up in the morning and stare at a blank piece of paper. I’d have no ideas, just like an ordinary person. You’ve set mathematics back a month.”

This quote is hilarious, and I find it interesting that there's a difference in intelligence between drug users and non users. My gut feeling is that there would be no significant difference.

I will note that most drug use does not impact intelligence negatively. Of course it can if abused to a great enough degree as that will significantly alter neural function but this also depends on the specific mechanisms of the substance.

Dr. Carl Hart is a great example of this. He's been a recreational heroin user for 5 years and is a tenured professor of neuroscience at Columbia.

https://en.m.wikipedia.org/wiki/Carl_Hart