Intoxication is the physical and mental impairment that occurs following alcohol consumption. This process unfolds progressively, directly related to the concentration of alcohol in the bloodstream, known as Blood Alcohol Concentration (BAC). BAC measures the percentage of alcohol circulating in the blood and is used by medical and legal professionals to define the stages of impairment. As BAC rises, the functional decline of the body and mind moves through a predictable series of stages.
The Physiological Basis of Impairment
Alcohol acts as a central nervous system (CNS) depressant, slowing down brain activity. When consumed, alcohol is rapidly absorbed, primarily through the small intestine, and distributed throughout the body’s water content. The effects of alcohol are mediated by its interaction with neurotransmitters.
Alcohol enhances the effects of gamma-aminobutyric acid (GABA), the brain’s main inhibitory neurotransmitter. Increasing GABA’s activity suppresses neuronal excitability, leading to a quieting effect on the brain. This suppression results in slowed reaction times, impaired judgment, and reduced motor coordination. Alcohol also inhibits NMDA receptors, which further contributes to cognitive and memory impairments during intoxication.
The Progressive Stages of Intoxication
The stages of intoxication are defined by the severity of CNS depression, which correlates with increasing Blood Alcohol Concentration levels. These stages are averages, and a person’s individual reaction can vary based on tolerance and other factors.
Subclinical/Euphoria (0.01 – 0.05% BAC)
The earliest stage of intoxication involves a BAC ranging from 0.01% to 0.05%. At this level, a person may feel mildly relaxed and lightheaded. Inhibitions are slightly loosened, and a mild sense of euphoria begins to emerge. Although the individual may not appear visibly intoxicated, minor impairment of reasoning and memory can be detected.
Excitement/Lethargy (0.05 – 0.15% BAC)
As the BAC rises into the 0.05% to 0.15% range, behavioral changes become noticeable, often including exaggerated emotions and slurred speech. Judgment is impaired, and motor skills degrade, affecting balance and vision. The legal limit for driving in most United States jurisdictions is 0.08% BAC, reflecting the motor and cognitive impairment that occurs in this range.
Confusion/Stupor (0.15 – 0.30% BAC)
A BAC between 0.15% and 0.30% marks a severe level of intoxication, leading to confusion and stupor. Physical symptoms include severe motor impairment, making it difficult to stand or walk without staggering. Nausea and vomiting are common, and the depressant effects become dominant, leading to drowsiness and disorientation. This stage often results in memory blackouts, where events are forgotten even if the person remains conscious.
Coma/Death (0.30%+ BAC)
When the BAC reaches 0.30% and beyond, the individual enters the coma stage. At 0.30% to 0.40%, a person will likely lose consciousness, and all mental, physical, and sensory functions are severely impaired. A BAC over 0.40% is considered fatal due to the severe suppression of the CNS. The risk of death is high because the respiratory system can shut down, leading to respiratory arrest.
Factors Influencing Blood Alcohol Concentration
The rate at which a person moves through these stages is influenced by several physiological variables, not solely the amount of alcohol consumed.
- Biological sex is a factor because women generally have less body water and higher body fat than men, which results in a higher BAC for the same amount of alcohol consumed.
- Body weight plays a part, as a person with a higher body weight generally has more body water available to dilute the alcohol.
- Consuming food before or while drinking slows the absorption of alcohol from the digestive tract into the bloodstream.
- Drinking quickly causes a rapid spike in BAC because the body can only metabolize alcohol at a relatively fixed rate, typically about one standard drink per hour.
- Genetic factors and certain medications can affect the metabolic rate of alcohol, altering how quickly the body processes the substance and influencing the resulting BAC.
Recognizing and Responding to Alcohol Poisoning
Alcohol poisoning represents an overdose of alcohol, demanding immediate medical intervention. The condition occurs when high BAC levels overwhelm the body’s ability to function. Key warning signs include confusion, seizures, and an inability to be roused or stay conscious.
A person with alcohol poisoning may exhibit slow or irregular breathing, defined as fewer than eight breaths per minute or gaps of more than ten seconds between breaths. Skin that is cold, clammy, or has a bluish or pale appearance indicates hypothermia. Vomiting is common, and the depressed gag reflex creates a risk of choking.
If alcohol poisoning is suspected, emergency medical services must be contacted immediately; the person should never be left alone or allowed to “sleep it off.” While waiting for help, the person should be placed in the recovery position—rolled onto their side—to prevent choking if they vomit. Stay with the person and monitor their breathing until medical professionals take over.