Can a clinical psychologist diagnose psychiatric diseases?

Yes: As a psychiatrist, i frequently rely on neuropsychological testing for adhd. They te conducted by psychologists.

Yes: Most state licensing laws allow clinical psychologists to diagnose "mental and nervous disorders" . Clinical psychologists probably vary more in terms of the settings and types of psychiatric disorders they trained with than psychiatrists do. Those well-trained will often do in-depth assessments with psychological testing. Psychiatrists will also emphasize ruling out medical disorders.

Yes: Both psychiatrists and psychologists use the Diagnostic and Statistical Manual 5th edition published by the American Psychiatric Association to diagnose patients.