Alcohol's Effects on the Body and Behavior
Alcohol is a central nervous system depressant. It slows reaction time, impairs judgment and coordination, and reduces inhibition. Effects rise with the amount consumed, the speed of consumption, and the person's body weight, sex, food intake, tolerance, medications, and health. Tolerance means a person can appear composed while still being impaired - a trap in questions that assume a "good drunk" is safe to serve.
Blood alcohol concentration (BAC) is the measure of impairment. For many adults, one standard drink raises BAC by roughly 0.02, and the body eliminates alcohol at roughly 0.015 to 0.02 per hour - slower for many people. This is why time is the only sobering agent. At higher BAC, effects progress from relaxation and talkativeness to impaired judgment and coordination, then to slurred speech, vomiting, blackouts, and finally to loss of consciousness and danger of alcohol poisoning. Signs of alcohol poisoning include unresponsiveness, slow or irregular breathing, cold or clammy skin, and vomiting - this is a medical emergency; call for help and do not leave the person alone.
Traps: assuming coffee, food, or a cold shower sobers someone; assuming a person who can walk is not impaired; and missing that combining alcohol with medication or other drugs magnifies effects.
Worked example: a guest who has had two drinks in an hour is on a prescription that causes drowsiness. The combined effect may be greater than the count suggests. Rule of thumb: count drinks, count time, and watch behavior - the body doesn't lie, but the guest might.