This varies widely from policy to policy. The mental health or behavioral health components of a person’s insurance coverage may or may not be covered by the same company that handles other medical issues. In many policies specific limits are set on the number of inpatient psychiatric days a person can have over the course of a year, or even over the course of a lifetime. Each insurance plan also specifies which practitioners and even facilities that they will reimburse.
In an attempt to create some equality, a law was passed in 1996, the Mental Health Parity Act. This law created a set of rules for group health plans whereby coverage for mental health could not be less than that for other medical conditions. In reality, this legislation is filled with loopholes, it does not apply to health plans with less than fifty-one employees, it does not state that a health plan even has to offer a mental health benefit (some do not), and it does not apply to federal and state programs such as Medicare and Medicaid. So you can never assume that just because you have health insurance it will cover mental health services.
The question of what is and what is not covered can become complicated and frustrating. Most hospitals, clinics, and private practitioners go through a pre-certification or pre-approval process, before starting services. They should let you know if you’re covered or not. Additionally, most health plans publish annual descriptions of their benefits that include lists of “in network,” or approved providers.