The majority of drugs act on the brain's "reward circuit," resulting in pleasure and flooding the brain with the chemical messenger dopamine. A well-functioning reward system encourages people to repeat acts that are necessary for them to thrive, such as eating and spending time with loved ones. Dopamine spikes in the reward circuit are what cause the reinforcement of pleasant but hazardous behaviours such as drug usage. Individuals are then compelled to repeat the activity.
When a person continues to use drugs, their brain adjusts by reducing the ability of cells in the reward circuit to respond to it. This will occur as long as the individual continues to consume drugs. This condition, known as tolerance, has the effect of reducing the individual's high in comparison to the high they had when they first took the drug. They might try to achieve the same high by ingesting more of the chemical. Because of these brain alterations, the individual frequently discovers that they are unable to get pleasure from other activities that they previously enjoyed, such as eating, sexual activity, or social activities.
Long-term use alters various chemical systems and circuits in the brain, which can affect a wide range of cognitive and behavioural functions, including learning, judgement, decision-making, stress, memory, and behaviour. Because of the nature of addiction, many people who use drugs continue to do so despite being aware of the potentially harmful effects of their actions.
Why do some people acquire a drug tolerance while others are able to avoid this fate? There is no one factor that can predict if a person would develop a drug addiction. A variety of factors influence the chance of acquiring an addiction. The more predisposing qualities a person exhibits, the more likely it is that consuming drugs will end in drug addiction.