-Dr. Nora Volkow, Director of the National Institute of Drug Abuse
Addiction is defined as a chronic, relapsing brain disease that is characterized by compusive drug seeking and use, despite harmful consequences. Addiction is a result of key changes in the brain, classifying it as a brain disease. When a drug is used, parts of the brain that are responsible for life-sustaining functions are altered, which in turn, drive the compulsive drug abuse.
How do drugs work in the brain?
Drugs corrupt the brain's natural communication system and change the way nerve cells function. Dopamine is the neurotransmitter that drugs try to replicate. Dopamine is the naturally occuring neurotransmitter that controls movement, emotion, cognition, motivation, and most importantly, feelings of pleasure. According to the National Institue of Drug Addiction (NIDA), drugs release 2 to 10 times more dopamine in the brain than natural rewards, such as food and love. This powerful reward motivates people to seek more drugs and continue to use them again and again. In order to gain the pleasure that a user experienced during their first use, they need to continually increase the dosage of the drug.
The image below compares the dopamine levels in the brain of an addict to the brain of a non-addict in response to natural rewards. The drug user does not receive the same levels of dopamine that a non-user receives, leading them to seek happiness in ways they know will guarantee a reward.
After repeated drug use, the brain loses its ability to communicate pleasure in any circumstance other than when the drug is used. As a result, the person will be unable to feel good about anything in their life without using the drug. Their brain is physically preventing them from feeling pleasure from any reward besides drug use. The person is no longer in control of their choices, because the brain is telling them to seek dopamine however they can find it, which in this case, is solely drug use. They need to take drugs in order to feel any sense of normalcy.
Studies have also shown that there are cognitive deficits associated with chronic drug abuse. For example, glutamate is another neurotransmitter that plays a role in the reward system. Using drugs alters the optimal concentration of glutamate in the brain, requiring the brain to overcompensate, causing impairments in cognitive functions. Time Magazine found that regular marijuana users "could lose 8 IQ points."
Long-term use can also dramatically affect judgment and behavior. In some cases, it can drive a compulsion to obtain and use nicotine, alcohol or other drugs, even when the individual knows the consequences are harmful or dangerous.
These changes in the brain can remain even after the person stops using substances. These changes leave those with addiction vulnerable to physical and environmental cues that they associate with substance use, also known as triggers, which can increase their risk of relapse.