As a person continues to abuse drugs, the brain adapts to the overwhelming surges in dopamine by producing less dopamine or by reducing the number of dopamine receptors in the reward circuit. As a result, dopamine’s impact on the reward circuit is lessened, reducing the abuser’s ability to enjoy the drugs and the things that previously brought pleasure. This decrease compels those addicted to drugs to keep abusing drugs in order to attempt to bring their dopamine function back to normal. And, they may now require larger amounts of the drug than they first did to achieve the dopamine high — an effect known as tolerance.
Additional Changes Drug Abuse Can Cause
Long-term abuse causes changes in other brain chemical systems and circuits as well.
• Damaged cognitive function. Glutamate is a neurotransmitter that influences the reward circuit and the ability to learn. When the optimal concentration of glutamate is altered by drug abuse, the brain attempts to compensate, which can impair cognitive function.
• Uncontrollable cravings. Drugs of abuse facilitate nonconscious (conditioned) learning, which leads the user to experience uncontrollable cravings when they see a place or person they associate with the drug experience, even when the drug itself is not available. Brain imaging studies of drug-addicted individuals show changes in areas of the brain that are critical to judgment, decision making, learning and memory, and behavior control.
Together, these changes can drive an abuser to seek out and take drugs compulsively despite adverse consequences—in other words, to become addicted to drugs.
Why Do Some People Become Addicted While Others Do Not?
No single factor can predict whether or not a person will become addicted to drugs. Risk for addiction is influenced by a person’s biology, social environment, and age or stage of development. The more risk factors an individual has, the greater the chance that taking drugs can lead to addiction. For example:
• Biology. The genes that people are born with — in combination with environmental influences — account for about half of their addiction vulnerability. Additionally, gender, ethnicity, and the presence of other mental disorders may influence risk for drug abuse and addiction.
• Environment. A person’s environment includes many different influences — from family and friends to socioeconomic status and quality of life in general. Factors such as peer pressure, physical and sexual abuse, stress, and parental involvement can greatly influence the course of drug abuse and addiction in a person’s life.
• Development. Genetic and environmental factors interact with critical developmental stages in a person’s life to affect addiction vulnerability, and adolescents experience a double challenge. Although taking drugs at any age can lead to addiction, the earlier that drug use begins, the more likely it is to progress to more serious abuse. And because adolescents’ brains are still developing in the areas that govern decision making, judgment, and self-control, they are especially prone to risk-taking behaviors, including trying drugs of abuse.
Prevention Is Key
Drug addiction is a preventable disease. Research has shown that prevention programs that involve the family, schools, communities, and the media are effective in reducing drug abuse. Although many events and cultural factors affect drug abuse trends, when people, particular youth, perceive drug abuse as harmful, they reduce their drug taking. It is necessary, therefore, to help youth and the general public to understand the risks of drug abuse and for teachers, parents, and health care professionals to keep sending the message that drug addiction can be prevented if a person never abuses drugs.