The DEA is the agency with most responsible for drug enforcement in the U.S. and also shares its responsibilities with the Federal Bureau of Investigation . It also has complete responsibility ( duty to do something ) for U.S. drug enforcement investigations in other countries . Not only is the DEA the lead agency for domestic enforcement of the Controlled Substances Act , sharing concurrent jurisdiction with the Federal Bureau of Investigation and Immigration and Customs Enforcement , it also has sole responsibility for coordinating and pursuing U.S. drug investigations abroad .