1.5 Neurobiology of Substance Use Disorders
Open Resources for Nursing (Open RN)
Severe substance use disorders, also called addictions, were once considered a moral failing or character flaw but are now known to be chronic illnesses. Scientific evidence shows that addiction to alcohol or drugs is a chronic brain disease that has potential for relapse and recovery.[1]
All addictive substances have powerful effects on the brain. These effects account for the euphoric or intensely pleasurable feelings that people experience during their initial use of alcohol or other substances. These feelings motivate people to use those substances again and again, despite the risks for significant harm. As individuals continue to misuse alcohol or other substances, progressive changes, called neuroadaptations, occur in the structure and function of the brain. These neuroadaptations drive the transition from controlled, occasional substance use to chronic misuse that can be difficult to control and can endure long after an individual stops using the substances. These changes can lead to the need for increased amounts of substances to achieve the same effect, referred to as tolerance. They may produce continued, periodic craving for the substance that can lead to relapse. More than 60 percent of people treated for a substance use disorder experience relapse within the first year after they are discharged from treatment, and a person can remain at increased risk of relapse for many years.[2]
For many people, initial substance use involves an element of impulsivity (i.e., acting without foresight or regard for the consequences). For example, an adolescent may impulsively take a first drink, smoke a cigarette, experiment with marijuana, or succumb to peer pressure and try a party drug like Ecstasy. If the experience is pleasurable, this feeling positively reinforces the substance use, making the person more likely to take the substance again. Another person may take a substance to relieve negative feelings such as stress, anxiety, or depression. In this case, the temporary relief the substance brings from the negative feelings reinforces substance use, increasing the likelihood that the person will use again.[3]
Many other environmental and social stimuli can reinforce a behavior. For example, peer approval positively reinforces substance use for some people. Likewise, if drinking or using drugs with others provides a feeling of relief from social isolation, substance use is reinforced.[4]
Eventually, in the absence of the substance, a person may experience negative emotions such as stress, anxiety, or depression or the individual may feel physically ill. This is called withdrawal, which often leads the person to use the substance again to relieve the withdrawal symptoms. As use becomes an ingrained behavior, impulsivity shifts to compulsivity, and the primary drivers of repeated substance use shift from positive reinforcement (feeling pleasure) to negative reinforce