U.S. spending on prescription drugs rose 8.5% last year, slightly less than in 2014, driven mainly by price hikes and growing use of costly new drugs.

Data firm IMS Health estimated that patients, insurers and federal payers spent a combined $309.5 billion last year on prescription medicines. The IMS Institute for Healthcare Informatics is forecasting that annual increases in U.S. prescription drug spending will slow to between 4% and 7% through 2020, after rising about 10% in each of the past three years. It predicts spending will reach $370 billion to $400 billion by 2020.