According to the Journal of American Medical Association (JAMA), 50 percent of the people who have a severe mental condition also have a substance abuse problem. The JAMA also found that 37 percent of alcoholics have a mental illness, as do 53 percent of drug addicts. These high rates make the relationship between mental health and drug abuse a strong one. Many studies have been performed to discover the reason for such a relationship. Although many studies are ongoing, mental health professionals have determined a few things about addiction and mental health:

• Undiagnosed mental illness can lead to substance abuse as the person tries to treat the symptoms of the mental condition. Depression, anxiety, paranoia and restlessness are some of the common symptoms that mentally ill addicts are trying to self-medicate.
• Diagnosed mental illness patients often take medication that has unpleasant side effects. These patients abuse drugs to alleviate those effects. For example, schizophrenia patients take medication for hallucinations that causes depression. The patients usually smoke marijuana to deal with the depression.
• A few drugs can cause mental illness after years of chronic abuse. Drugs such as ecstasy alter chemicals in the brain that control mood and other behaviors. These alterations can lead to depression or anxiety problems that the addict treats with other drugs.
• People who are at risk for mental illness increase that risk when they chronically abuse drugs. Mental health risk factors include genetics, the environment, major life experiences and other things. People who already have high risk factors can be “pushed” into the mental illness by chronic substance abuse.
• Heavy drug abuse in the adolescent years can lead to mental illness later. Heavy drug abuse can alter the cognitive and social development of teens, two things are formulated during adolescence. When these factors are altered, depression and anxiety disorders can result. (http://drugabuse.com/library/mental-health-and-drug-abuse)