A popular acid reflux medication was the costliest drug paid for by Medicare Part D in 2013, while a blood pressure medication was the most frequently prescribed, according to a new Centers for Medicare & Medicaid Services report on prescription drug prices.

A new drug dataset the agency published provides detailed information on more than one million distinct healthcare providers who collectively prescribed $103 billion in prescription drugs under the Part D program that year.

The costliest drug to the Part D program in 2013 was Nexium. There were more than 8 million claims processed for the medication, totaling more than $2.5 billion, CMS reported. (Advair, Crestor and Abilify were second- , third- and fourth-most costly, respectively.) More than 36.8 million claims for Lisinopril, a blood pressure drug, were processed in 2013, the agency added, making it the most frequently prescribed by Medicare Part D physicians.

Pharmaceutical Research and Manufacturers of America (PhRMA), which lobbies for the industry, criticized the CMS report, claiming it mischaracterized actual Part D spending because it didn’t account for rebates. The American Medical Association called it “complex.”

President Obama has asked Congress to make it legal to allow Medicare to negotiate prices with drug manufacturers as one way to rein in consumer drug prices, while calling on pharmaceutical companies to develop more “precision” drugs to specifically target life-threatening illnesses.

Approximately 36 million people, or 68% of all Medicare beneficiaries, are enrolled in the Part D program, CMS says. According to the American Society of Consultant Pharmacists, seniors consume 40% of prescription drugs. On average, individuals 65 to 69 years old take nearly 14 prescriptions per year, the group adds, while individuals aged 80 to 84 take an average of 18 prescriptions per year.