According to Quest Analytics, the drug positivity rates in 2018 of people in the US who were subjected to urine drug tests as a condition of employment are:
Federally Mandated Safety-Sensitive Workforce: 2.7%
General US Workforce: 5.1%
Combined US Workforce: 4.4%

Click here for the complete datatable of Drug Positivity Rates Of US Employees Subjected to Urine Drug Tests, by Worker Category