Most are diagnosed by Psychiatrists; some by psychologists. For certification purposes, only psychiatrists can diagnose.

Psychiatrists are specialists qualified to diagnose and certify mental disorders. In the process they may need help with diagnostic tests and assessments. MPhil qualified Psychologists are licensed practitioners who can perform these tests or assessments and help in certification or diagnosis of mental disorders. In most cases Psychiatrists are able to make independent diagnosis but in certain cases they ask for psychological tests to guide the diagnosis.

A psychiatrist can diagnose mental illnesses as they are specialised in this field

A Psychiatrist diagnose mental illness