There are severe consequences associated with a drug addiction. The more the individual uses drugs and alcohol, the guiltier he will feel, and the more depressed he will become. He will sacrifice his personal integrity, his relationships with friends and family, his job, his savings and anything else he may have in an attempt to get more drugs. His relationships and job performance will go drastically downhill.
In addition to the mental stress created by this unethical behavior, the drug addict's body has also adapted to the presence of the drugs. He will experience an overwhelming obsession with getting and using the drugs, and will do anything to avoid the resulting pain when withdrawing from them. This is when the new drug addict begins to experience drug cravings. He now seeks drugs both for the "pleasure" they give him and to avoid the mental and physical horrors of withdrawal. At this point, the drug addict is stuck in a vicious dwindling spiral. The drugs he abuses have changed him both physically and mentally.
There is such a thing as a "drug personality," which is basically artificial and solely created by drug consumption. Drugs can change the attitude of a person from his original personality to one secretly harboring hostilities and hatreds he does not allow to be seen on the outside. Such types of personalities helps us to establish a link between drugs and increasing difficulties with crime, production and the modern breakdown of social and industrial culture.
When the addict initially tries to quit, cells in the brain that have become used to large amounts of these metabolites (the substances the body converts the drugs or alcohol into and that get trapped in the fatty tissues) are now forced to deal with much decreased amounts. Even as the withdrawal symptoms subside, the brain "demands" that the addict give it more of the drug. This is called drug craving. Craving is an extremely powerful urge and can cause a person to create all kinds of "reasons" they should begin using drugs or drinking again. He is now trapped in an endless cycle of trying to quit, craving, relapse and fear of withdrawal.
Eventually, the brain cells will again become used to having lowered drug metabolites. But, because deposits of drug or alcohol release back into the bloodstream from fatty tissues for years, craving and relapse remain a cause for concern. Left unhandled, the presence of metabolites even in microscopic amounts cause the brain to react as if the addict had again actually taken the drug and can set up craving and relapse even after years of sobriety.