Used needles litter the ground outside an abandoned building where many addicts live in Kabul, Afghanistan.

Photo Paula Bronstein/Getty Images

Substance Abuse

Different substances produce different levels of highs, hangovers, addictions and cravings. Some will produce few physical withdrawals but strong cravings. Others can do just the opposite. Some addiction researchers have concluded that psychological dependence is the more extreme of the two, as it has more widespread consequences for both the person (by destroying personal relationships) and society at large (through crime committed to get drugs).

There are a wide variety of substances that a person can become addicted to. In 21st-century America, some of the worst and most often used drugs are:

  • Methamphetamines - prolonged use of this stimulant can lead to psychotic-like symptoms such as strong hallucinations and violent behavior. Studies of the brain patterns of some long-term meth users have shown that up to 50 percent of their dopamine-producing cells have been damaged. Use of meth has declined from 2001 to today [source: DEA].
  • Prescription medications - this is one of the rapidly growing substances of abuse in the United States. Between 1980 and 1998, abuse of prescription drugs increased 400 percent. It has about the same amount of usage in America as cocaine [source: NIDA].
  • Heroin - In 2005, 2.4 percent of the American population said they had tried heroin at least once [source: Department of Health]. Heroin withdrawal symptoms are particularly painful and can come on just a few hours after a dose wears off. Because of this, users have a high chance for relapse; in 2004, the entrance rate for heroin treatment for the fifth time or more was higher than the entrance rate for first-time heroin treatment [source: NIDA].
  • Alcohol - physicians consider alcohol more dangerous to suddenly withdraw from than even heroin, due to the physical symptoms that come along with alcohol withdrawal. In 2003, there was an estimated 18 million alcoholics in the United States [source: NIAAA]. Alcoholics are also prone to relapse; in 2004, 22 percent of alcoholics in the United States who sought treatment had been in rehab for alcohol at least one other time [source: NIDA].

It's not just substances that a person can become addicted to. Behaviors like eating and sex can become compulsive in some people. Although someone addicted to a behavior experiences the same flux of dopamine, when the compulsive behavior is stopped, he will not experience physical symptoms like a substance abuser. Still, the effects compulsive addictions can have on a person's life can be just as devastating. Some of the most common compulsive behaviors are:

  • Sex addiction - characterized by an overly intense sex drive or an obsession with sex. A sex addict will engage in risky sexual behavior, even at the cost of his relationships or health. He may have a number of affairs, but will have trouble forming bonds or even enjoying the act. When treating sexual addiction, the goal is not abstinence, but a return to non-harmful sexual behavior.
  • Food - food addiction is called binge-eating disorder. It's much like bulimia, but rather than binging on and purging food compulsively, the food addict only binges. An estimated 2 percent of people in the United States had a binge eating disorder in 2005 [source: Anred].
  • Gambling - there were an estimated 2-million-plus gambling addicts in the United States in 2002. Just as with a drug, a gambling addict gets a rush from the act of betting. He will also lose control of his ability to not bet. Unlike treatment for sex or food addictions, abstinence is considered the goal of rehab for gambling addiction [source: Biotie].

In the next section, we'll learn what science is doing to fight addiction.