Improving Access to Mental Health Act This bill amends title XVIII (Medicare) of the Social Security Act to: (1) increase the Medicare reimbursement rate for clinical social worker services, (2) exclude clinical social worker services from the prospective payment system in which predetermined amounts form the basis for payment under Medicare, and (3) alter the definition of “clinical social worker services” as it relates to Medicare. Under current law, “clinical social worker services”: (1) include services performed for the diagnosis and treatment of mental illnesses, and (2) exclude services furnished to an inpatient of a skilled nursing facility as a condition of the facility's participation in the Medicare program. The bill repeals these provisions and instead specifies that such services include certain types of health behavior assessment and intervention.