From the summary:
In the last decade, numerous states have made drug screening and testing an eligibility condition for Temporary Assistance for Needy Families (TANF) cash assistance under certain circumstances. As of November 2015, 13 states have adopted such regulations. Wisconsin included a provision in its state budget to screen and test certain individuals participating in FoodShare Employment and Training under the Supplemental Nutrition Assistance Program (SNAP). Legislatures in 19 other states have recently considered bills to drug test under TANF.
Very few applicants have tested positive for drug use in states that have implemented these policies. Consequently, operating costs far exceed the fiscal savings from denying benefits. This is consistent with previous research that found only a small share of welfare recipients experience substance abuse disorders.