"If a substantial portion of the observed drop in [worker's compensation] claims [after implementation of the PADT - post-accident drug testing program] is driven by underreporting, however, PADT’s net effect on the Company and its employees is less clear. Not only may the administration of the PADT program itself be costly to the Company, but unreported workplace hazards could fester and, over the long term, impose even higher costs. Meanwhile, PADT may make accident reporting so costly for some workers that they opt to pay for medical care out-of-pocket or simply endure injuries that would otherwise be treatable through workers’ compensation. If many workers are covered by health insurance plans—particularly if they are covered on a family member’s plan—the costs of treatment could be shifted from the Company onto other benefits providers."

Source

Morantz, Alison D., & Mas, Alexandre, "Does Post-Accident Drug Testing Reduce Injuries? Evidence from a Large Retail Chain," American Law and Economics Review (Cary, NC: American Law and Economics Association, August 23, 2008) , Vol. 10, No. 2, p. 296.
http://www.princeton.edu/~ama…