Many people don’t understand why or how other people become addicted to drugs. They may mistakenly think that those who use drugs lack moral principles or willpower and that they could stop their drug use simply by choosing to do so. In reality, drug addiction is a complex disease, and quitting usually takes more than good intentions or a strong will. Drugs change the brain in ways that make quitting extremely difficult, even for those who want to.

Addiction is a chronic disease characterized by

seeking and use, despite an awareness of the negative consequences.

Because addiction is a chronic disease, people can’t simply stop using drugs for a few days and be cured. Most patients need long-term or repeated care to stop using completely and recover their lives.

What happens to the addict’s brain?

Most drugs affect the brain’s “reward circuit” by flooding it with the chemical messenger dopamine. This reward system controls the body’s ability to feel pleasure and motivates a person to repeat behaviors needed to thrive, such as eating and spending time with loved ones. This overstimulation of the reward circuit causes the intensely pleasurable “high” that can lead people to take a drug again and again.

As a person continues to use drugs, the brain adjusts to the excess dopamine by making less of it and/or reducing the ability of cells in the reward circuit to respond to it. This reduces the high that the person feels compared to the high they felt when first taking the drug—an effect known as tolerance. They might take more of the drug, trying to achieve the same dopamine high. It can also cause them to get less pleasure from other things they once enjoyed, like food or social activities.

  • learning
  • judgment
  • decision-making
  • stress
  • memory
  • behavior

Addiction + Mental Illness

Many people who are addicted to drugs are also diagnosed with other mental disorders, and vice versa. Compared to the general population, people addicted to drugs are roughly twice as likely to suffer from mood and anxiety disorders, with the reverse also true. This does not mean that one caused the other, even if one appeared first.

Research suggests the following possibilities for this common co-occurrence:

  • Drug abuse may bring about symptoms of another mental illness.
  • Mental disorders can lead to drug abuse, possibly as a means of “self-medication.”
  • Overlapping genetic vulnerabilities.
  • Overlapping environmental triggers such as stress or trauma.
  • Involvement of the stress and reward brain regions in both addiction and mental disorders.
  • Drug use disorders and other mental illnesses are developmental disorders. This means that they often begin in the teen years or even younger—periods when the brain experiences dramatic developmental changes. Early exposure to drugs of abuse may change the brain in ways that increase the risk for mental disorders. Also, early symptoms of a mental disorder may indicate an increased risk for later drug use.


Source: National Institute on Drug Abuse; National Institutes of Health; U.S. Department of Health and Human Services.