The economic impact of the Mental Health Parity and Addiction Equity Act, which requires larger employer-based insurance plans to cover psychiatric illnesses and substance use disorders in the same way they do illnesses such as cancer and multiple sclerosis, has been minimal, a new study finds.

Yale University researchers studied the first year of the law’s implementation, and found it did not result in a rise in the proportion of enrollees seeking treatment for substance use disorders, according to Medical Xpress. They found there was an increase of $10 annually per health plan enrollee in spending for substance use disorder treatment.

The law was passed in 2008 and went into effect for most plans in 2010. Before the law was passed, health plans often imposed limits on treatments for substance use disorders, such as restricting the number of visits, and requiring higher cost-sharing, the article notes. While the measure was being debated in Congress, some health plans and employers warned it would significantly increase their costs.

“To my knowledge this is the first peer-reviewed study to examine the effects of the 2008 federal parity law on substance use treatment,” lead researcher Susan Busch of the Yale School of Public Health, said in a news release. “The small increase in per-enrollee spending suggests plans are unlikely to drop coverage for [substance use disorder] treatment in response to the law.”

The study appears in the American Journal of Managed Care.