Often simply referred to as alcohol, ethanol is the active ingredient in alcoholic beverages. Its simplicity makes it sneak across membranes and nestle into many different parts, producing a wide range of effects compared to other clunkier molecules. So how exactly does it cause drunkenness? Why does it have dramatically different effects on different people? To answer these questions we will need to follow alcohol on its journey through the body.
Alcohol lands in the stomach and is absorbed into the blood through the digestive tract especially the small intestine. The contents of the stomach impact alcohol’s ability to get into the blood because after eating the pyloric sphincter which separates the stomach from the small intestine closes, so the level of alcohol that reaches the blood after a big meal might only be a quarter that from the same drink on an empty stomach. From the blood alcohol goes to the organs especially those that get the most blood flow, the liver and the Brain, it hits the liver first and enzymes in the Liver breakdown the alcohol molecule in tow steps, first an enzyme called ADH turns alcohol into acetaldehyde which is toxic, then an enzyme called ALDH converts the toxic acetaldehyde turn on toxic acetate. As the blood circulates the Liver eliminates alcohol continuously but this first part of elimination determines how much alcohol reaches the brain and other organs.
Brain sensitivity is responsible for the emotional, cognitive and behavioral effects of alcohol, otherwise known as drunkenness, alcohol turns up the brain’s primary brake, the neurotransmitter GABA and turns down its primary gas the neurotransmitter GLUTAMATE. This makes neurons much less communicative and users feel relaxed at moderate doses, fall asleep at higher doses and can impede the brain activity necessary for survival at toxic doses. Alcohol also stimulates a small group of neurons that extend from the midbrain to the Nucleus Accumbens a region important for motivation.
Like all addictive drugs, it prompts a squad of dopamine in the Nucleus Accumbens which gives users a surge of pleasure. Alcohols also cause some neurons to synthesize and release endorphins. Endorphins help us to calm down in response to stress or danger. Elevated levels of endorphins contribute to the euphoria and relaxation associated with alcohol consumption.
Finally, as the liver’s breakdown of alcohol outpaces the brain’s absorption, drunkenness fades away. Individual differences at any point in this journey can cause people to act more or less drunk, for example, a man and a woman who weigh the same and drink the same amount during an identical meal will still have different blood alcohol concentration or BAC. This is because women tend to have less blood. Women generally have a higher percentage of fat which requires less blood than muscle. A smaller blood volume carrying the same amount of alcohol means the concentration will be higher for women. Genetic differences in the liver’s alcohol processing enzymes also influence BAC, and regular drinking can increase the production of these enzymes contributing to tolerance.
On the other hand, those who drink excessively for a long time may develop liver damage, which has the opposite effect.
Meanwhile, genetic differences in Dopamine, GABA and endorphins transmission may contribute to risk for developing an alcohol use disorder. Those with naturally low endorphin or dopamine levels may self-medicate through drinking. Some people have a higher risk of excessive drinking due to a sensitive endorphin response that increases the pleasurable effects of alcohol. Others have a variation in GABA transmission it makes them especially sensitive to the sedative effects of alcohol which decreases the risk of developing disorder drinking.
Meanwhile, the brain adapts to chronic alcohol consumption by reducing GABA, Dopamine and Endorphins transmission and enhancing Glutamate activity this means regular drinkers tend to be anxious, have trouble sleeping and experience less pressure. These structural and functional changes can lead to disordered use when drinking feels normal but not drinking is uncomfortable establishing a vicious cycle. So both genetics and previous experience impact how a person experiences Alcohol. Which means that some people are more prone to certain patterns of drinking than others and a history of consumption leads to neural and behavioral changes.