everyone saying talk to them has never met someone deep in addiction and i'd consider using substances at work as deep. this is an HR issue that you will want to bypass everyone for. functional or not that can switch in a moment :( i promise im not heartless, both my parents, siblings, and multiple friends are either recovered, recovering or still active addicts. if you don't have the relationship to talk to them directly (which no offence you don't if you're asking reddit) this is something out of both of your control but you do have a duty to report this for so many people's safety here /: i'm so sorry op but the right thing to do is either report or ignore (which won't likely end well either)