The question of whether a person is still intoxicated when suffering from a hangover is a common source of confusion, largely because the unpleasant symptoms feel similar to being drunk. Both states can involve dizziness, nausea, and poor coordination, leading many people to believe the alcohol is still actively affecting the brain. The physical distress of a severe hangover can easily be mistaken for continued intoxication. Understanding the difference requires separating the presence of alcohol in the body from the residual effects of the body’s struggle to process it.
Defining Intoxication vs. Hangover
Intoxication is defined by the active presence of ethanol, the alcohol consumed in beverages, in the bloodstream. This is quantitatively measured by Blood Alcohol Content (BAC), which represents the mass of alcohol per unit of blood volume. While intoxicated, the ethanol itself is directly interfering with neurotransmitters in the central nervous system, leading to characteristic effects like impaired judgment and slurred speech.
A hangover, by contrast, is a collection of physical and psychological symptoms that occur after the acute intoxication phase has passed. The symptoms typically begin when the BAC starts to fall significantly and often peak when the BAC is at or near zero. Therefore, in most cases, a person is not still “drunk” when they are hungover because the intoxicating chemical, ethanol, has largely been removed from the body.
The Alcohol Metabolism Timeline
The body processes alcohol through a two-step enzymatic pathway primarily located in the liver. First, the enzyme alcohol dehydrogenase (ADH) converts the consumed ethanol into a highly toxic compound called acetaldehyde.
Acetaldehyde is then rapidly broken down by a second enzyme, aldehyde dehydrogenase (ALDH), into harmless acetic acid, which the body can easily excrete. The rate at which the liver can perform this process is relatively constant across individuals, averaging a BAC decline of about 0.015% per hour, which roughly corresponds to one standard drink per hour. This steady pace ensures that once drinking stops, the intoxicating ethanol is systematically cleared from the system.
What Causes Hangover Symptoms
The lingering pain and discomfort of a hangover are caused by a cascade of physiological stresses that persist even after the alcohol is gone. One major factor is the diuretic effect of alcohol, which increases urine production and leads to significant dehydration. This fluid loss contributes to common symptoms like thirst, dry mouth, and the throbbing headache.
Alcohol consumption also triggers an inflammatory response as the immune system releases pro-inflammatory molecules called cytokines. These compounds are linked to general malaise, fatigue, headache, and nausea, making the body feel acutely ill. The gastrointestinal system suffers direct irritation from ethanol, which increases stomach acid production and inflames the stomach lining, resulting in nausea and stomach pain.
Furthermore, the initial toxic intermediate, acetaldehyde, can cause residual cellular damage that lasts into the next day. Poor sleep quality also contributes significantly, as alcohol disrupts normal sleep cycles, preventing the restorative deep and REM sleep the body needs.
Residual Impairment and Practical Safety
While the blood alcohol content may be zero, the presence of a hangover still results in measurable functional impairment. Research confirms that cognitive functions, such as attention, memory, and reaction time, are noticeably degraded in a hungover state. This means the ability to focus on complex tasks or recall information is significantly compromised.
Motor skills and psychomotor speed are also negatively affected, leading to poorer coordination and slower reaction times than when completely sober. Studies have shown that the impairment in driving ability during a hangover can be comparable to the impairment seen at a low but legally measurable BAC. Therefore, while a person is not legally intoxicated, the severe reduction in mental and physical capabilities makes activities like driving or operating heavy machinery highly unsafe.