 The new law significantly increased federal regulatory authority over drugs by mandating a pre-market review of the safety of all new drugs, as well as banning false therapeutic claims in drug labeling without requiring that the FDA prove fraudulent intent.Soon after passage of the 1938 Act, the FDA began to designate certain drugs as safe for use only under the supervision of a medical professional, and the category of "prescription-only" drugs was securely codified into law by the 1951 Durham-Humphrey Amendment.These developments confirmed extensive powers for the FDA to enforce post-marketing recalls of ineffective drugs.