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How do drugs affect the brain?

During Active Addiction

For the brain, the difference between normal rewards and drug rewards can be described as the difference between someone whispering into your ear and someone shouting into a microphone. Just as we turn down the volume on a radio that is too loud, the brain adjusts to the overwhelming surges in dopamine (and other neurotransmitters) by producing less dopamine or by reducing the number of receptors that can receive signals. As a result, dopamine’s impact on the reward circuit of the brain of someone struggling with addiction can become abnormally low, and that person’s ability to experience any pleasure is reduced. This medical condition is called “anhedonia”. It is also present in people with depression.

This is why a person who is struggling with addiction eventually feels flat, lifeless, and depressed, and is unable to enjoy things that were previously pleasurable. The person needs to keep taking drugs in an attempt to bring his or her dopamine function back up to normal so they feel normal – which only makes the problem worse, like a vicious cycle. Also, the person will often need to take larger amounts of the drug to produce the familiar dopamine high – an effect known as tolerance.

Addicted Brain Response

Decreased Dopamine Transporters in a Methamphetamine Misuser

The same sort of mechanisms involved in the development of tolerance can eventually lead to profound changes in neurons and brain circuits, with the potential to severely compromise the long-term health of the brain. For example, glutamate is another neurotransmitter that influences the reward circuit and the ability to learn. When the optimal concentration of glutamate is altered by drug misuse, the brain attempts to compensate for this change, which can cause impairment in cognitive function. Similarly, long-term drug misuse can trigger adaptations in habit or non-conscious memory systems. Conditioning is one example of this type of learning, in which cues in a person’s daily routine or environment become associated with the drug experience and can trigger uncontrollable cravings whenever the person is exposed to these cues (called “triggers”), even if the drug itself is not available. This learned “reflex” is extremely durable and can affect a person who once used drugs even after many years of abstinence.

Chronic exposure to alcohol or other drugs disrupts the way critical brain structures interact to control and inhibit behaviors related to drug use. Just as continued misuse may lead to tolerance or the need for higher drug dosages to produce an effect, it may also lead to addiction, which will drive a user to seek out and take drugs compulsively. Drug addiction erodes a person’s self-control and ability to make sound decisions, while producing intense impulses to take drugs.

Post Addiction Withdrawal Syndrome (PAWS)

Stopping drug use doesn’t immediately return the brain to normal. Some drugs have toxic effects that can kill neurons—and most of these cells will not be replaced. While changes to connections between neurons in the brain may not be permanent, some last for months. Some research suggests the changes may even last for years.

Long-lasting brain changes can make it challenging for individuals struggling with addiction to stay drug-free. They often experience intense cravings for years, which can lead to relapse. However, the brain has neuroplasticity. That means it can repair itself, over time.

For further information and discussion, see:

FAR would like to thank Dr. Meldon Kahan for reviewing the Addiction section of this website for accuracy.