WASHINGTON — A Senate report released Thursday lays out systematic failures in the reporting system for suspicious opioid orders, faulting some drug distributors and manufacturers for their roles and criticizing the Drug Enforcement Administration for a years-long lull in enforcement actions.

The findings, the latest in a series of reports from Sen. Claire McCaskill (D-Mo.), the top Democrat on the Senate’s leading oversight committee, pointed in particular to disparities between two leading drug distributors: McKesson and AmerisourceBergen.