According to About Alcoholism Guide, BuddyT, nearly half of all alcoholics have an overlapping mental illness. Further, at least 50 percent of the 2 million Americans with severe mental illness abuse illicit drugs or alcohol, compared to 15 percent of the general population. Clearly alcohol and drug abuse are often a complication to mental illness.
When depression or other mental illness is coexistent with alcohol or drug abuse this is known as "dual diagnosis". If the abuse is a result of the mental illness, it may also be referred to as "self-medication", meaning that the person is using the drug as a means of coping with the symptoms of their illness.
Because it is easy to obtain and doesn't have the same social stigma that illegal drugs do, alcohol is one of the most popular drugs chosen for self-medication. Rather ironically, alcohol is classified as a depressant and can accentuate many of the symptoms of depression. It can also interfere with a person's ability to successfully resolve the very situations that may have originally caused their depression.
In addition, alcohol is incompatible with many of the drugs used to treat depression. It can intensify the sedative effects of tricyclic antidepressants, such a Elavil. (1) Chronic alcohol consumption can increase the availability of some antidepressants while decreasing the availability of others. (2,3) Tyramine, a substance found in beer and wine, can interact with MAOIs potentially causing a dangerous in blood pressure. (4) Consult your physician or pharmacist for specific precautions regarding your own medications.
There is much debate as to whether one drug of abuse, marijuana, might actually help depression. Participants in a 1997 pilot study (5) reported that one of the reasons they continued to smoke marijuana was that they felt it relieved their symptoms of depression and anxiety. Another study (6) found that marijuana did not seem to exacerbate depression, but rather was another symptom of the condition. Although there is preliminary evidence that marijuana may have antidepressant properties, many argue there are also some important drawbacks to it's usage. There is a well-known phenomenon called "amotivational syndrome" in which chronic cannabis users become apathetic, socially withdrawn, and perform at a level of everyday functioning well below their capacity prior to their marijuana use. Although the depressed person may feel relief from their symptoms, this may be an illusion of well-being if the person loses motivation and productivity. Furthermore, if the drug is smoked, it can be far more harmful to the respiratory system that tobacco use because of the fact that it is not filtered.