WASHINGTON — Medicare is subsidizing drug abuse by thousands of beneficiaries who shop around for doctors and fill prescriptions for huge quantities of painkillers and other narcotics far exceeding what any patient could safely use, Congressional investigators say in a new report.

The investigators, from the Government Accountability Office, said Medicare officials had been slow to recognize and act on the evidence of abuse, which is to be presented at a Senate hearing on Tuesday.

“Our analysis found that about 170,000 Medicare beneficiaries received prescriptions from five or more medical practitioners” for 14 types of drugs that are frequently abused, said Gregory D. Kutz, director of forensic audits and special investigations at the accounting office.

The medications were obtained through Part D of Medicare, which provides coverage for prescription drugs. The drugs most commonly abused by Medicare beneficiaries included powerful prescription painkillers like oxycodones and hydrocodone products. Oxycodones include OxyContin and Percocet.