Stimulants aren't my scene so I don't really know how prevalent they are in tech (but it's never been in my face, at least not compared to when I was in high school). However, marijuana and alcohol are freaking everywhere. Second week at a big company and I had a coworker showing me, among other things, pictures of his pot plantation. Plenty of folks vaped at work (some to the extent that they were incapable of doing their jobs).

As for alcohol, San Francisco is a hard drinking town. In other countries if you get a cocktail it will be very carefully measured. Here? Outside of some artisan hipster joints you get hilariously unbalanced drinks. We had a drug/alcohol free policy at work but still had a beer fridge or two. Off-sites were generally open bar. 1:1 meetings? Often at the nearest bar (which typically lasted 1-2 drinks). Weekly team off-site lunches? Booze. First day on the job? Let's go to Kozy Kar (ugh) to celebrate with our high profile investor. Friday night? Let's go to Martuni's and get blitzed. CEO is too drunk to stand? Don't worry he's still good to drive. Hardly Strictly with the coworkers? Sure, let's make a pitcher of margaritas first.