What's the difference between a psychiatrist and a psychologist?

Psychiatrists are medical doctors who can diagnose, prescribe medication, and manage physical aspects of mental illness. Psychologists hold graduate degrees in psychology and provide assessment and psychotherapy; in most places they don't prescribe.

A reasonable rule: psychiatrist first for severe symptoms, suspected bipolar disorder or psychosis, significant functional collapse, or when medication is likely needed.

Psychologist first for mild to moderate anxiety, low mood, relationship or stress difficulties. Many people see both, and they often work together.