PBM Oversight Act of 2023 This bill requires prescription drug plan (PDP) sponsors under the Medicare prescription drug benefit to report certain information about the involvement of affiliated committees in decisions about formularies. Specifically, PDP sponsors that use formularies must report to the Centers for Medicare & Medicaid Services the names and descriptions of committees that are affiliated with the PDP sponsor, or a contracted pharmacy benefit manager, that are authorized to change initial recommendations of the pharmacy and therapeutic committee about formularies. PDP sponsors must also report any formulary changes that were made by an affiliated committee and provide justifications for these decisions. The Government Accountability Office must report on the use of these types of committees with respect to formularies under the Medicare prescription drug benefit, including decision-making trends.