Of the developers/tech folks I know it's mostly a weed/booze crowd. A few people that do party drugs. And a few people who occasionally do psychedelics. No one I know seems to have any outwardly visible issues with it. I do know one person who I am sure has problem with painkillers, but it's that scary blurry ground between "addict" and "chronic pain sufferer". I don't think it effects her work, but I wonder about their personal life.

Also stimulants. I almost forgot to mention them because they are basically water in this industry. Almost everyone who isn't on some sort of health kick is using some combo of caffeine/amphetamine derivatives/coke/modalert/etc.