While average out-pocket costs grew for most people last year, women age 19 to 25 saw no difference in their average out-of-pocket medical costs, primarily as a result of Obamacare, according to HCCI.

The Affordable Care Act mandates that insurance plans cover the cost of contraceptives without co-payments from enrollees.

That was the main reason that young adult women's total average out-of-pocket costs didn't budge from $662 last year, even though their use of contraceptives grew by 4 percent, Frost said.

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"This is the first time we have seen flat out-of-pocket spending growth by any group of the privately insured," Frost said. "They paid more for some services, at the same time they spent less for contraceptives."

The HCCI report found that spending per broad categories of medical services remained in line with what was found in prior reports.

Acute in-patient admissions accounted for 20 percent of spending, out-patient care was responsible for 28 percent of expenditures, and 34 percent of the spending went to professional services. The remaining 17 percent went toward prescription medication.

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Health-care spending up despite lower use