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What’s Happening In Your Brain?

How Common Substances Do What They Do

Alcohol can suppress your inhibitions, caffeine can keep you awake and nicotine can make your heart beat faster.

These effects all happen in the brain, but how exactly do they work?

Paul Carvey, PhD, neuropharmacologist and chairperson of the Department of Pharmacology at Rush University Medical Center, explains:

Alcohol is a paradox. Since it’s a depressant, you’d think the first drink would start slowing you down. But alcohol facilitates the effect of a neurotransmitter called gamma-aminobutyric acid (GABA). Neurotransmitters carry chemical messages between nerves, and GABA functions as an inhibitor in the brain. So initially, alcohol depresses the brain functions, such as judgment, that keep us in check.

“It’s like taking your foot off the brake,” says Carvey.

Alcohol also increases the release of another neurotransmitter dopamine, creating feelings of pleasure.

After a few more drinks, alcohol starts depressing other brain functions, such as balance and reaction time. Depending on the drinker’s weight, general health and how recently he or she ate, too much alcohol at one time can depress the central nervous system and eventually lead to death.

Caffeine, on the other hand, is a stimulant. It blocks the effects of a substance called adenosine that works in the thalamus — the main information switchboard of the brain. Normally, adenosine gradually shuts down the thalamus throughout the day, making us less alert. With caffeine, the switchboard connections stay open, and concentration and alertness are enhanced.

Every person responds to caffeine differently, but for some people too much caffeine can cause headaches, nervousness and irritability, as well as disrupted sleep.

Nicotine is also a stimulant. In the brain and other organs, it attaches to receptors for the neurotransmitter acetylcholine, because of their similar shapes. These receptors are then activated by both acetylcholine and nicotine — creating extra stimulation for functions such as respiration, heart rate and alertness. Nicotine also causes pleasurable feelings by boosting the release of dopamine.

If you’re wondering how something you ingest will affect you, be sure to ask your doctor, especially if you take any medications. Your doctor can tell you about any potential interactions.


Paul Carvey, PhD, is a professor and dean at the Graduate College of Rush University. His research focuses on dopamine and its relationship to Parkinson’s disease, and he has participated in numerous National Institutes of Health studies and grants.


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