Drugs tap into the brain's communication system and disrupt the way nerve cells normally send, receive, and process information. Drugs work in the brain by:
- Imitating natural neurotransmitters (chemical messengers in the brain). Because of the similarity in chemical structure between drugs and neurotransmitters naturally produced by the brain, some drugs, such as marijuana and heroin, are able to "fool" the brain's receptors and activate nerve cells to send abnormal messages via the network.
- Overstimulating the reward system by flooding the circuit with dopamine. Dopamine is a neurotransmitter present in regions of the brain that regulate movement, emotion, motivation, and feelings of pleasure. And nearly all drugs of abuse, directly or indirectly, activate this system. Some drugs, particularly stimulants like methamphetamine and cocaine, cause nerve cells to release abnormally large amounts of natural neurotransmitters or prevent their normal recycling, which is needed to shut off the signal between neurons.
What happens to your brain if you keep taking drugs?
- The brain adapts. In response to the overwhelming surges in dopamine, the brain adjusts by decreasing the number of dopamine receptors available– thus diminishing the function of the reward circuit. Drug addicts are compelled to abuse drugs to bring their dopamine function back up to normal, requiring ever larger amounts to achieve the initial dopamine high– an effect known as tolerance.
- Changes in neurotransmitters other than dopamine. Long-term abuse causes changes in other brain chemical systems, including glutamate, 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 cause impairment in cognitive function.
- Drug abuse can trigger nonconscious memory systems.Conditioning is one example of this type of learning, whereby environmental cues, such as certain people or places, become associated with the drug experience and can trigger uncontrollable cravings if the individual is exposed to these cues, even without the drug itself being available
- Addiction. Brain imaging studies of drug-addicted individuals show changes in areas of the brain that are critical to judgment, decisionmaking, learning and memory, and behavior control. These changes are likely what drive an abuser to seek out and take drugs compulsively despite adverse consequences.
