Drugs and alcohol cause a massive surge of neurotransmitters in the brain, which is what leads to feelings of inebriation. This feeling can be overwhelming and unpleasant for some people, especially in excess, but for someone with a propensity for addiction, it’s incredibly pleasant. It can also be a welcome feeling for those who are struggling with an untreated mental health condition.
If someone finds the experience pleasurable and rewarding, their brain takes note and reminds them to do it again. One flaw of the human brain is that it doesn’t differentiate between an experience you enjoy that’s good for you or one that’s harmful. A substance use disorder occurs when a person continues to use the substance excessively to chase that sensation.
As time goes by, they need an increasing amount to achieve the desired results, and their life becomes focused on obtaining, using and recovering from inebriation. Eventually, when a SUD is severe, the individual’s field of interest revolves almost exclusively around drugs or alcohol. Science currently says that this is because the brain is so fixated in on the reward it perceives it can get from substances that it loses sight of other potential sources of pleasure and motivation.