The mental health parity law passed in 2008, but it didn't cover people in smaller health plans.

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The Obama administration delivered on a long-delayed health care promise when it issued rules to ensure equal health insurance treatment for people with mental health and substance abuse problems.

The rules, issued Friday, require that most health insurance plans offer the same amount of coverage for mental health and substance abuse claims as they do for medical and surgical coverage.

That means insurers can't charge someone more for mental health services than for other services. It used to be that plans could â€" and would â€" pay 80 percent for medical care but only 50 percent for mental health care. But under these rules, plans can't cover fewer inpatient hospital days for mental health or substance abuse treatment than they do for a physical illness.

The law creating what's called mental health "parity" actually passed in 2008. Mental health advocates have been agitating for these rules ever since.

That's because once the Mental Health Parity and Addiction Equity Act barred insurance companies from imposing limits on the number of hospital days or copayments, insurance companies started looking for other ways to limit mental health and substance abuse care, like requiring preauthorizations that they don't demand for other medical care. That won't be allowed anymore. These rules also clarify coverage for rehabilitation or other intermediate types of care that don't fall neatly into inpatient or outpatient categories.

Until recently, the mental health parity law only applied to people covered by large group health plans â€" those with more than 100 workers.

That all changed when the Affordable Care Act was passed in 2010. It expands parity requirements to include smaller group and individual plans. And it also requires that those plans cover mental health and substance abuse.

But that last requirement wasn't included in the 2008 law, and it still doesn't apply to larger plans under the Affordable Care Act. The 2008 law just says if the plan offers coverage, that coverage has to be the same for mental health and substance abuse as it is for other medical care.

So more people are covered, but there are still some people who are left out. While Medicare now has a mental health parity requirement, Medicaid and the Children's Health Insurance Program don't.