Drug abuse is defined as using a legal, illegal or non-medical substance for the purpose of achieving a "high". This can occur when a person takes a prescribed medication in ways that are not prescribed, when a person uses over the counter medication inappropriately to manufacture other substances such as meth-amphetemine, or when persons use cocaine, marijuana, heroine, LSD, etc...for the purpose of getting high.
Drug dependence has two forms: psychological and physical. Drugs that cause physical dependency are known to be addictive substances. These are narcotics, pain medications, opioids, alcohol, and meth-amphetemine. Marijuana is known to cause psychological dependency. That means, the user will not experience physicla withdrawal symptoms if the drug is not available.
Alcoholism is the use of alcohol in such a way that it interferes with the other life functions of the user in a negative manner. Alcoholism is known as the disease of being addicted to alcohol. The disease model of treating the addiction to alcohol has been very successful and helpful in education addicts about the nature of the substance, the causes, and the avoidance of further damage due to addiction. Alcoholism has been shown to have some genetic linkages. Alcohol is a drug that is legal for consumption by persons in the U.S. age 21 and up. So, it is possible to be addicted to alcohol and still remain at a job as long as no legal issues result related to the consumption of alcohol.