Drug-Free Workplace Statements are not a required element of Policies for non-government organizations. There are, however, good reasons to include this policy in your Employee Handbook. Drug abuse, alcoholism, and prescription drug addiction are all too common in our society. Additionally, these afflictions may present in any gender, age, race, religion or income stratum.
If your apostolate happens to be in one of the four states (and District of Columbia) in the United States which allows the use of recreational marijuana, or one of the states which allows medically prescribed cannabis products, the language of the policy may need to be adjusted to reflect these statutes
This article, from the law offices of Gordon and Rees in Washington State, is worth reading if you are situated in one of these states.