A rather disreputable source, Buzzfeed News, says
The DEA is limited by statute to enforcing drug-related federal crimes. But on Sunday, Timothy Shea, a former US attorney and close confidant of Barr's who was named acting administrator of the DEA last month, received approval from Associate Deputy Attorney General Bradley Weinsheimer to go beyond the agency’s mandate “to perform other law enforcement duties” that Barr may “deem appropriate.”
So far, the only other mentions of this I can find cite Buzzfeed News as their source.
But my question(s) are: If this statute exists, where is it? and is it legal for such an approval to be given by anyone other than Congress? I was unable to find such a limitation in in Title 21.