Drug testing
The Drug Detection Agency in NZ conducted over 100,000 tests on jobseekers and employees in 2014. Almost 6% of tests came back positive (despite improvements in the construction and forestry industries). And Cannabis was responsible for 83% of the positive results.
Given the likelihood of greater abuse in companies where tests are not being conducted it does suggest that employers everywhere should be seriously concerned about this level of abuse.
But to test you need an enabling clause in your employment agreement and a supportive policy.