(Based in part on this NYT Article)

Short-Term Effects on the Brain and Body

Alcohol (ethanol) quickly affects the brain by increasing dopamine, which creates pleasurable feelings, and altering GABA (enhancing) and glutamate (inhibiting), which slows brain activity. It also activates endogenous opioids which further contribute to central nervous system depression. This leads to relaxation, lowered inhibitions, impaired judgment, and reduced motor control. At very high levels, alcohol can suppress brain activity enough to cause unconsciousness or even death. These effects vary among individuals due to factors such as genetics, frequency of use, body weight, other drugs, overall health, etc., but as a general rule, if you are feeling any effects (buzz, sleepy, etc.) from alcohol, then your brain chemistry is under the influence of alcohol. In some studies, brain function is affected at very low blood alcohol levels (.01-.05%), which although “subliminal” in terms of psychoactive effect, may affect things such as reaction time and judgement.

How Effects Increase with Dosage

In effect, alcohol works from “the top down” in the brain, starting with higher cortical functions and proceeding all the way to the brain stem, which is responsible for autonomic functions such as heart rate and respiration.

Blood Alcohol Level	Effects	Brain Region Affected
Low (0.02–0.05%)	Relaxation, mild euphoria	Prefrontal cortex (inhibition relaxed)
Moderate (0.05–0.10%)	Impaired judgment, slowed reflexes	Frontal lobes, cerebellum
High (0.10–0.20%)	Slurred speech, poor coordination	Cerebellum, motor cortex
Very high (0.20–0.30%)	Confusion, stupor	Limbic system, wider brain
Dangerous (0.30%+)	Loss of consciousness, respiratory depression	Brain stem (life-threatening)[1]

Alcohol’s Effect on Mood

For many people, alcohol initially can “improve” mood with dopamine induced euphoria and reduced inhibitions, which can seem to support social interaction and sense of wellbeing. Central nervous system depression can also feel like calm and even temporary relief from anxiety and worry. As blood alcohol levels increase, the increased disinhibitory effect can lead to more “outlandish” or regrettable behavior including things such as promiscuity, self-endangerment, rage, and aggression among other behaviors, which is often not remembered once the alcohol is metabolized out of the body. This is because ethanol also affects the limbic system, and in particular the hippocampus, which is where memories are made and stored.

Next day effects on mood often include anxiety, irritability, brain fog, fatigue, regret, and low mood. The toxic effects of ethanol and acetaldehyde on the body such as headache, nausea, “cotton mouth,” and other symptoms also tend to have a depressive effect on mood. Research suggests that people who are hungover may also have more difficulty regulating emotions. In some cases, dopamine levels don’t just return to baseline, they actually go below baseline as the brain attempts to regain homeostasis, resulting in mood being lower than it was before using alcohol.

Several factors contribute to these emotional hangovers:

• Neurotransmitter rebound as the brain returns to baseline after alcohol’s effects
• Disrupted sleep, since alcohol reduces REM sleep
• Dehydration, which may affect mood
• Memory impairment, which can lead to worry about regretted behaviors

Long-term effects:
Ethanol and its metabolite, acetaldehyde, are toxic to living cells. Over time, regular alcohol use can harm multiple body systems:

• Brain: Associated with reduced brain volume over time, possibly due to inflammation and damage to neurons.
• Mouth and throat: Alcohol is converted to acetaldehyde, a carcinogenic compound that damages DNA and increases the risk of cancers of the mouth, throat, larynx, and esophagus.
• Heart and cardiovascular system: Alcohol temporarily dilates blood vessels but regular use can raise blood pressure, increase risk of hypertension and atrial fibrillation, and may raise breast cancer risk in women due to increased estrogen levels. Evidence on moderate drinking and heart attack or stroke risk remains mixed.
• Digestive system: Alcohol can cause acid reflux, stomach inflammation, intestinal damage, and increased risk of colorectal cancer.
• Liver and Pancreas: The liver metabolizes alcohol and is especially vulnerable, while a byproduct of ethanol, acetaldehyde, can cause severe inflammation and cellular destruction in the pancreas. Heavy drinking can lead to fatty liver disease, inflammation, fibrosis, cirrhosis, and liver cancer as well as both acute and chronic pancreatitis. Early damage to both organs can sometimes be reversed if drinking stops.

Research suggests that chronic alcohol use can also change the brain’s base-line neurotransmitter levels resulting in both neural hypo and hyperactivity with sudden cessation of drinking. This can lead to multiple symptoms from irritability, anxiety, depression and panic to tremors. In terms of withdrawal from severe chemical addiction, some detox symptoms such as seizure are significant enough to require medical interventions.

Risk levels
Although there is likely no completely safe amount of ethanol, health risks are generally low at about one drink per day or less, but risks increase significantly with heavier drinking (around 8–14 drinks per week or more). In short, any level of inebriation indicates likely pathological effects on brain and body. Genetics and existing health conditions also influence how alcohol affects individuals. Reducing or stopping heavy drinking can reverse some of the damage.

Corrupted Cognitive Data

One very significant, but often overlooked problem with regular use of alcohol to intoxication is that while inebriated, even at modest levels, all of the “data” that is compiled by the brain is corrupted—every conclusion, memory, feeling, belief, sensory perception, etc. occurs during an altered state and is therefore at some level incomplete, inaccurate, or simply wrong. But it doesn’t end there. Even when we are no longer “under the influence,” we continue to access the same corrupted data from when we were inebriated to draw new conclusions, modify memories, confirm or deny beliefs, interpret feelings, solve problems, etc. This phenomenon at least partly explains the experience of growing clarity that heavy drinkers experience over extended periods of sobriety.

Summary

Alcohol can produce short-term pleasurable effects but carries increasing health risks with greater and longer-term consumption, affecting the brain, cardiovascular system, digestive tract, and liver & pancreas among other organs. It also often creates deleterious effects on mood and emotional health.

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[1] Alcohol can be life threatening at relatively low blood alcohol levels even if the brain stem continues to support basic biological functions due to factors such as car accidents, self-endangerment, and suffocation from vomiting.