Because it's illegal. Kinda like why you'd get suspended for running a dog fighting ring or illegal possession of firearms. If you don't like the law, you can fight it. But it's still illegal. Yeah, it's a much bigger issue than sports. And yes, company costs DO play a role. Anyone who could be a health insurance liability is a potential target. Alcoholism is a protected sacrament in this country, mainly because alcohol is legal. And I think its time will come. Obesity is the target next on the horizon. Illegal activities at work should be dealt with harshly, I agree. I don't think the issue is just productivity and fewer accidents. Although, if the threat of testing and dismissal is present, I'd bet that an employee is less likely to partake in an activity that could have lingering effects that diminish their capacity to produce. If an employee on a business trip, at a convention, etc, etc, does something illegal, and gets caught, that reflects on the company. Regardless of the employees "on the clock status." If an employee goes straight from work to the bar, gets drunk, and crashes and kills someone, that too, is a reflection on the company. Whether it's fair or not, media spin and public perception make it so. What a person does in their own time is their own business, yes. But those activities aren't guaranteed to not cross the doorstep at 8AM when their shift starts, or never interrupt their business day. Also, there's a study from UofTex (here) that indicates (in a small sample size) that there's a significant chance of use of other illegal drugs (greater than 40%) for those who use marijuana, and in their study that illegal drug use without marijuana use was much smaller (warning really, really, really small sample). The validity of that data can be argued, but it's data that confirms the hypothesis. It's going to take a lot of data indicating any other result, to change the minds of most.