Depression and anxiety are common symptoms presented by patients with mental illness. The primary care provider can be a good source for treating these conditions when only anti-depressants and anti-anxiety medications are needed. However, while these treatments may be effective for some people for a period of time, a psychiatrist can identify the root problem manifesting as depression and anxiety and treat the root rather than the symptom. For example,

• Problems in the workplace, family relationship problems, or marital problems may present as depression. The primary care provider will usually treat depression with anti-depressant medications, whereas counseling provided by a psychiatrist is geared to discover the underlying cause. Anti-depressants may be needed for a time but medication in conjunction with counseling provides a more effective treatment.
• A person diagnosed with bipolar disorder may not look for treatment while in a manic or hypomanic phase, but when he begins to have depressive symptoms he may seek treatment from his primary care provider.  If bipolar disorder is diagnosed in the early stages, a mood stabilizer prescribed by a psychiatrist can be a better treatment option than an antidepressant medication which may cause further manic episodes and subsequent hospitalization.
• A person with psychosis may hear voices, or exhibit paranoid or delusional behavior. He may seek care from his primary care provider who will most likely treat his symptoms of depression with anti-depressants which may actually increase the symptoms of psychosis. A psychiatrist is trained to diagnose these symptoms and treat appropriately.
• A person with substance dependence may present to his primary care provider for treatment to alleviate his symptoms of depression and anxiety which manifest when he is unable to get his drug of choice.  A more proper treatment option is detox with a rehabilitation program and proper counseling which can be given by a psychiatrist. 

The primary care physician is not trained to diagnose and treat mental illness.  A psychiatrist is the professional care provider who can adequately diagnose and treat mental disorders.