Drug addiction causes physical effects in the brain as well as psychological effects. Different types of drugs cause different reactions in the brain. The question “How does drug addiction affect the brain?” has been studied by scientists for decades, but some of the deepest effects are only becoming clear in recent years.
Drugs as Neurotransmitter Mimics
Many drugs mimic natural neurotransmitters in the brain. These natural chemicals lead to pleasurable feelings, such as relaxation and euphoria, so drugs that mimic specific neurotransmitters cause similar effects. Heroin, prescription opioids and marijuana all work in ways similar to neurotransmitters.
Some types of drugs manipulate natural levels of neurotransmitters instead of mimicking those chemicals directly. Cocaine blocks the receptors for the neurotransmitter dopamine, which causes that chemical to build up in the brain instead of being processed normally. This accumulation of dopamine causes the euphoric feelings associated with cocaine use.
Stimulants such as methamphetamine operate by causing neurons in the brain to release extra dopamine and norepinephrine. These drugs also prevent the brain from breaking down those chemicals, leading to a buildup that causes an intense high.
Reward Systems in the Brain
Drug use manipulates the brain’s reward system, the chemical processes that cause people to repeat pleasurable activities associated with survival. Most of the neurotransmitters affected by drugs are part of this system. Normally, these neurotransmitters cause you to find pleasure in survival-related things, such as food and sexual activity. Drugs that target these neurotransmitters tie pleasurable sensations to drug use.
Tolerance and Drug Use
Over time, the brain adapts to drug use by changing the levels of natural neurotransmitters produced by neurons. Dopamine receptors become less sensitive and the brain produces less natural dopamine because there is so much already around. This makes it harder to achieve feelings of euphoria and relaxation, so drug users have to start taking more to achieve the same effect.
As drug tolerance develops, it can also reduce the ability to feel pleasure from normal activities, since normal dopamine levels have been skewed by drug use. This sometimes leads to drug users increasing their drug use in an attempt to feel normal again.
Withdrawal and the Brain
Some drugs cause withdrawal symptoms when you stop using them because the brain has become reliant on the drug. The lack of artificial neurotransmitter stimulation causes feelings of anxiety, irritability and discomfort. Some people have trouble quitting drugs because of these withdrawal symptoms. Taking the drug can ease the symptoms, which makes breaking the drug addiction cycle more difficult.
Long-Term Effects of Drugs on the Brain
In addition to the short-term effects, drug use also has long-term effects on the brain. Some drugs affect the parts of the brain that handle decision making, memory, impulse control and learning. Heavy drug use over a long time period can permanently damage the brain.