U.S. consumers’ health-care costs fell in May for the first time in almost four decades, the latest evidence that government policies and an expansion in generic drugs are holding back prices.

The Labor Department’s price index for medical care — a figure that includes individuals’ outlays for insurance, medical supplies, doctor visits and hospital stays — fell a seasonally adjusted 0.1% in May. The leading driver of last month’s drop was a 0.6% contraction in prescription-drug costs.

The dip came as overall inflation across the economy remained moderate, rising a seasonally adjusted 0.1% during the month, a reflection of the slow recovery that has contained product prices and wages for years.

The latest turn in consumers’ medical costs, in figures released Tuesday, follows decades of steady gains in health-care costs from technological advances and increased use of health services. The last time medical costs posted a monthly decline, the patent on the modern MRI machine was a year old and the first test-tube baby was three years from being born. That was 1975.