The Obama administration will finalize a rule Friday that will require insurers to treat mental health and substance abuse problems the same way as physical illness, according to an administration official.

The regulation--which will be jointly issued by the Health and Human Services, Labor and Treasury Departments—will ensure that co-pays, deductibles and visit limits for mental illness and addiction treatment will be comparable to surgical and medical benefits. The administration official who described the measure asked not to be identified because the announcement had not been made yet.