Mental health disorders are diagnosed by healthcare or mental health professionals with various qualifications:

  • Psychiatrists (medical doctors who specialize in the field of psychiatry)
  • Primary care doctors
  • Psychologists
  • Psychiatric or mental health nurses or nurse practitioners
  • Social workers
  • Licensed professional counselors
  • Marriage and family therapists or couples therapists
  • Other mental health practitioners, such as counselors, therapists, neuropsychologists, cognitive-behavioral therapists, addiction specialists, psychoanalysts, pastoral counselors, and sex therapists

There's a gray area between dealing with an emotional difficulty—such as a loss in the family or a major life tragedy—and having a mental health disorder. A doctor or therapist can't run lab tests or read an x-ray to pin down a depression or anxiety diagnosis. Instead, mental health professionals have to be detectives of sorts. They read clues from the patient's behavior, draw conclusions from thoughts and feelings the patient might be having, and interpret certain physical signs and symptoms. For an official diagnosis, mental health professionals can compare these clues to a set of official guidelines that define each mental health disorder. These guidelines are outlined in a diagnostic manual used throughout the psychiatric and mental health community.

In the diagnostic manual, each condition has been labeled and described in a way that mental health professionals generally agree upon. The manual is updated periodically to reflect new medical knowledge and emerging research into human behavior. For example, outdated editions of the manual listed homosexuality as a mental disorder. Now, however, it is understood to be a normal part of the spectrum of human sexuality.