There are many important individual factors and circumstances that affect blood alcohol concentration (BAC) levels.
The faster an individual drinks, the quicker their peak BAC will raise and the more quickly they will become intoxicated. The liver metabolizes alcohol at a rate of approximately one standard drink per hour; 12 oz. beer, 5 oz. wine, .5-ounces or a "shot" of 80-proof distilled spirits or liquor (e.g., gin, rum, vodka, or whiskey). If more than one drink per hour is consumed, the liver is unable to keep pace and more alcohol will circulate in the blood stream until the liver can catch up. The more alcohol in the blood, the higher the intoxication level.
On average men have 76 c.c. of blood /kg body weight and in women it is 66 c.c. of blood /kg body weight. Not only do men have more blood in which to dilute alcohol by virtue of their greater size but even men of the same weight as women have slightly more blood in which to dilute alcohol. This is because muscle tissue contains more water than fat tissue, so men -- who have more muscle and less fat on the average than women -- can have about 10 percent more water in their bodies.
It is commonly thought that higher altitudes will cause intoxication more quickly than at sea level. Studies for the Federal Aviation Administration do not confirm the common belief. Additionally, for those living at higher altitudes the body compensates for the thinner air by producing more blood in which to carry oxygen. More blood by weight provides more dilution of alcohol.
About 20 percent of alcohol is absorbed into the bloodstream directly through the walls of the stomach and 80 percent is absorbed into the bloodstream through the small intestine. When there is food in the stomach, alcohol is absorbed more slowly into the bloodstream. Food in the stomach slows the absorption of alcohol by preventing it from going directly to the small intestine which is where the majority of alcohol enters the blood stream. The effects of the alcohol will still occur but at a slower rate.
It is a myth that food absorbs the alcohol. It does not. Drinking on a full stomach slows the absorption of alcohol because the stomach's pyloric valve, which connects the stomach and small intestine, closes to allow food to digest. The closed pyloric valve keeps alcohol in the stomach longer before it enters your small intestines.
It follows that fatty foods are more effective in slowing alcohol absorption than are other foods because they are more difficult to digest. Carbohydrates are passed through the stomach more quickly causing both the food and alcohol to enter the small intestines more quickly than with high fat content foods.
The pylorus valve may also go into spasm in the presence of concentrated alcohol, trapping the alcohol in the stomach instead of allowing it through to the small intestine. The drinker who downs several straight shots in an effort to get a quick high may actually experience a delayed effect.
Generally, the higher the alcohol concentration of a drink the faster the alcohol will be absorbed into the blood stream. One standard drink of hard liquor does have the same alcohol content as a regular beer. Since hard liquor is frequently less diluted (as in a shot) the effects will be noticed more rapidly.
The concept of a standard drink, that is 12 oz. beer, 5 oz. wine, .5-ounces or a "shot" of 80-proof distilled spirits or liquor (e.g., gin, rum, vodka, or whiskey) is often not a good guideline for judging your own BAC.
No two bartenders pour the same amount of alcohol and party hosts frequently pour more "Doubles" and drinks made with more than one type of liquor typically contain much more alcohol than the Standard Drink.
Water and fruit juices mixed with alcohol slow the absorption process, while carbonated beverages will speed it up. Carbonated drinks speed alcohol through the stomach and intestine into the bloodstream, creating a more rapid rise in BAC.
Medications can amplify the effects of alcohol on your body. Aspirin, tranquilizers, anti-depressants, and cough medicines to name only a few can effect when mixed with alcohol.
Long term drinkers develop tolerance to alcohol. One reason is that the liver becomes more efficient at metabolizing alcohol. In people with high tolerance to alcohol it takes more alcohol to produce the outward signs of intoxication. BAC is not affected by alcohol tolerance. Someone with higher alcohol tolerance is not safer to drive according the law.
Alcohol has a more pronounced effect on those who may be fatigued or under stress. Since alcohol is a depressant, someone who is depressed will likely become more depressed when drinking.