Psychiatrists focus exclusively on mental health. You may see a psychiatrist if you believe you have symptoms of mental illness. People usually seek out psychiatrists themselves, but some PCP's now are adding mental health screenings to yearly checkups, and may provide a referral. Psychiatrists can specialize in more than one mental illness, and can also specialize in treating substance abuse. Psychiatrists can informally specialize in specific age groups, though some informally prefer to work with different ages and on different illnesses as they gain experience with patients.