Five years after the Mental Health Parity and Addiction Equity Act of 2008 was signed by President George W. Bush, experts say the law has not created parity for mental health coverage.

The New York Times reports the law 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.

The rules guiding mental health coverage remain unclear, according to mental health patient advocates. Both they and health insurance companies say part of the blame lies with the federal government, which has not yet written the Parity Act’s final regulations for insurance companies. The Obama Administration has said it will draft rules by the end of this year.

There is often a dearth of accepted medical evidence on the best way to treat many mental illnesses, the article notes. “It’s very different from the approach to a bypass procedure or a hip replacement,” Karen Ignagni, CEO of America’s Health Insurance Plans, a trade association representing the nation’s health insurers, told the newspaper.

While simple treatments such as prescriptions for depression medication or short-term therapy are often covered by health insurers, they are more reluctant to cover more extended, complicated treatments such as months of residential care or frequent meetings with therapists.

The Parity Act applies to employer-sponsored health plans with 50 or more employees, and Medicaid managed care plans. Under the law, plans are not mandated to offer addiction and mental health benefits, but if they offer such benefits, they must do so in a non-discriminatory manner. That means a plan must have the same co-pays, deductibles and annual and lifetime caps on medical/surgical benefits and mental health/addiction benefits covered by the plan. Health plans cannot medically manage mental health/addiction benefits more stringently than they manage medical benefits.