The day marked a milestone for mental health advocates across the country who have been waiting five years since President George W. Bush signed the mental health parity law for its patient protections to go into effect.

“This final rule breaks down barriers that stand in the way of treatment and recovery services for millions of Americans,” Health and Human Services Secretary Kathleen Sebelius said in a press release.

The law generally prohibits insurers from requiring people to pay more out of pocket for mental health services than they would for care of physical problems or from imposing more restrictive limits on how often they can see a therapist.

In Massachusetts, implementation is partly underway.

Last year, the Legislature required all insurers regulated by the state — including plans for individuals, small businesses, and Medicaid recipients — to submit a report each year certifying that they have complied with state and federal parity requirements.

Last month, the state Division of Insurance collected those reports, which include information about how insurers were complying with interim regulations the Obama administration had released in 2010. This week, the state asked insurers to provide more information, including a detailed accounting of how often they have approved or denied coverage for medical and mental health services, said Deputy Commissioner Kevin Beagan.

The federal rules will extend protections to people covered by self-insured plans, typically offered by large employers and not regulated by the state.

State-regulated insurers must send a notice to customers by Jan. 1 explaining their rights to equal coverage and a new state process for filing a grievance if they believe they have wrongfully been denied mental health care.

With those steps and the state’s near-universal health insurance coverage, Massachusetts is seen as further ahead than many states in providing access to mental health care. But advocates here say there is plenty to be done.

The state Office of Patient Protection last year reviewed about 80 cases in which a patient was denied coverage for inpatient mental health care. By comparison, there were fewer than 20 other inpatient cases, related to medical or surgical care, for which the office considered appeals. The number of appeals related to behavioral health care is down slightly in the past three years.

On Friday, state mental health advocates and regulators were still sorting out just what changes the final federal rule will require.

Matt Selig, executive director of Health Law Advocates in Boston, which represents people who have been denied coverage, said the rule has at least provided certainty. Insurers can no longer cite its pending status as a reason not to fully comply.

“Now it’s in black and white,” he said.

The rule requires insurers to cover intermediate mental health services, or treatment that must be done on an inpatient basis but is not considered emergency care. Selig said that should help with cases his office often sees in which someone who needed residential treatment for an eating disorder or substance abuse is denied coverage or allowed too few days in the hospital.

Insurers are now required to release more information about how they make determinations about whether a person’s treatment is medically necessary.

“Health plans need to fully disclose how they are making coverage decisions, so consumers can have confidence that they’re not being discriminated against,” Selig said.

Parity is not as simple as saying that if a plan allows 12 visits to a physical therapist for a sprained ankle, it must allow the same number of visits to a psychotherapist for a mental illness. The rule applies to what are referred to as “nonquantitative treatment limitations,” or limits on the general scope or duration of care.

Ron Honberg, director of policy and legal affairs for the National Alliance on Mental Illness, said the rule stipulates that, if an insurance plan provides extensive rehabilitation services and case management for someone who has suffered a stroke, it must also cover an array of rehabilitation services for someone with schizophrenia.

Such aspects of the law will probably be clarified in further rulemaking and some will be sorted out in court, as individuals and insurers debate claims.

“There’s no doubt that this rule is not going to be the last word,” Honberg said.