Overview
Hangovers refer to the unpleasant feelings and physical symptoms that start shortly after the levels of the substance in the body return to almost zero, most commonly in reference to alcohol, where the symptoms include:
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Headaches, thirst, and dry mouth: alcohol blocks the release of vasopressin, an antidiuretic hormone that inhibits the reabsorption of water by the kidneys (which is why you feel the need to urinate so much when drinking) which leads to dehydration that shrinks the brain volume and puts tension on the membranes that connect the brain to the skull. This also produces the effects of dehydration throughout the body.
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Muscle aches: alcohol causes the body to release cytokines that provoke inflammation throughout the body which adds pressure directly to the peripheral nervous system and produces muscle aches comparable to ones found from having the flu
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Extreme fatigue and weakness: The liver prioritizes metabolizing alcohol by consuming a vital coenzyme called NAD+, which stops the production of new glucose and leads to low blood sugar that starves the body’s muscles of their primary energy mechanisms. Alcohol is also known to be damaging to the mitochondria, affectionately known as the “powerhouse of the cell” that synthesizes ATP for energy.
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Dizziness: Alcohol changes the properties of the fluid within the canals of your inner ear, and it takes time for these to rebalance even after alcohol has left your system, which confuses the tiny hair cells responsible for spatial orientation and can cause you to feel dizzy despite being perfectly still. Plus, with the dehydration, your body has less blood overall, which means your heart struggles to pump enough to the brain. This causes a drop in blood pressure, which also leads to dizziness.
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Nausea, vomiting, and stomachaches: Ethanol irritates the lining of the stomach, which causes an overproduction of gastric hydrochloric acid that destroys the layers of protective mucous. Further, ethanol is broken down by the liver into acetaldehyde, which is considered up to 30 times more toxic to the human body than ethyl alcohol and can trigger the brain’s receptors for nausea and vomiting.
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Anxiety and irritability: Alcohol mimics GABA, the brain’s primary neurotransmitter for calming the nervous system, while blocking glutamate, the brain’s primary neurotransmitter for exciting the nervous system. The brain compensates by weakening its GABA receptors and flooding itself with glutamate, which then produces anxiety, panic, and irritability.
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Shakiness, sweating, and rapid heartbeat: As noted above, glutamate floods the brain while drinking, which can feel psychologically like anxiety and irritability, but physically it also leads to tremors and shakiness. It’s very common to hear about those with alcohol use disorder who have “shaky hands” in the morning until they have a “hair of the dog.” Alongside glutamate, the body floods itself with stress hormones like cortisol and epinephrine, or adrenaline, that’s responsible for the fight-or-flight response from the sympathetic nervous system.
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Sensitivity to light and sound: flooding the nervous system with glutamate also makes it difficult for the sensory cortex of the brain to filter for important signals among background noise, so even small sounds and lights are interpreted as overwhelming inputs.
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Difficulty concentrating: Alcohol blocks Rapid Eye Movement (REM) sleep during which the brain achieves actual rest