Historically, authorities scheduled fentanyl analogs individually, which allowed for slightly modified and unscheduled variants to be distributed faster than they could be controlled . While "blanket" scheduling of fentanyl analogs by governing bodies like the United States Drug Enforcement Administration have helped limit the rise of new modified versions , their high potency has allowed them to permeate the drug supply chain as components in increasingly complex samples , complicating both law enforcement and public health responses .