Can you join the sheriff's department if you've done hallucinogens?

My boyfriend tried shrooms in Amsterdam (where it's legal!) last year. He did a very small dosage, and has only smoked pot once before. He is interested in joining the sheriff's department. Will this get in the way? I hear there's a magic number...like the number of times you've done drugs, how long ago it was, etc. He doesn't want to lie on his lie detector test (he's a super honest person), so he's going to be honest about it. Will he be okay?