How was Mike Tyson allowed to fight on drugs?

Question

In an interview he said he smokes grass everyday and smoked even before the fight. Don’t boxers take drug tests? How are they allowed to fight without being sober.

Answer 1

There's no drug tests for an exhibition fight, he could have been taken HGH and it wouldn't have made a difference.  This wasn't a sanctioned fight, it was a charity match.

Answer 2

Not if it is going to effect the box office take from a match that in the grand scheme is for expedition purposes only. It's not like Mike is coming out of retirement to compete.