It might be worse than a waste of money, actually. It would tend to repel smart people.
I remember once talking to a smart hacker who was leaving a big co where he'd worked for a while. He said he was leaving because they'd instituted drug testing. He himself didn't use any illegal drugs. He was quitting because it was a sign the company had become terminally lame.
The only reason companies do drug testing is because insurance companies will cut them deals. By the time your company is big enough that you can save millions of dollars in insurance costs by drug testing your employees, I hope you still have a soul.
Having said that, anyone dumb enough to fail a drug test is probably not a good person to hire anyways. Drug tests are easy to pass -- don't do any of the following drugs for a week and drink a lot of water, continuously, on the day of your test.
I remember once talking to a smart hacker who was leaving a big co where he'd worked for a while. He said he was leaving because they'd instituted drug testing. He himself didn't use any illegal drugs. He was quitting because it was a sign the company had become terminally lame.