Because alcohol changes the way the brain processes information, it also makes it difficult for people to make suitable decisions or assess their own behavior. For example, people who are very drunk might underestimate how intoxicated they are. Some might not even know that they are drunk. BAC is a measure of how much alcohol is in a person’s blood. This number represents a blood alcohol percentage. For example, a BAC of 0.05 means that the person’s blood is 0.05% alcohol.
For most people, the effects of alcohol at various levels of drunkenness are as follows:
- BAC below 0.06: A person may not notice any effects, or they might experience slight changes in mood. Some people feel relaxed or sleepy. Coordination and reflexes begin to decline.
- BAC 0.07–0.09: People may feel relaxed. They may feel more talkative or euphoric and less inhibited. In most states, having a BAC of 0.07–0.09 means that a person is legally drunk and cannot safely drive.
- BAC 0.09–0.15: At this point, a person may begin slurring their speech. They may still feel happy and euphoric, though some people feel sick. Reaction times are much slower, and a person may stumble. Driving is now unsafe.
- BAC 0.16–0.30: At this level of intoxication, a person is severely impaired. They may have very poor judgment, be unable to remember everything that happens, and be unable to fully understand the consequences of their actions. They may vomit or blackout and are at risk of alcohol poisoning.
- BAC 0.30–0.39: A person likely has alcohol poisoning. Their situation may be life threatening.
- BAC 0.40–0.50: A person may lose consciousness. Their body temperature may drop and their heart rate may change. The heart is in danger of stopping or failing. The risk of a coma is high.
- BAC 0.50+: The risk of death is very high, especially if the person does not receive immediate medical attention. Their heart may stop.
The amount of alcohol a person drinks is the biggest predictor of BAC. The more a person drinks, the higher their BAC will be. However, other factors also affect BAC. According to the 2015 National Survey on Drug Use and Health, 70.1% of adults in the United States report drinking alcohol during the past year. Heavy drinking tends to cause more serious intoxication and may eventually cause serious health issues, such as blackouts or kidney failure.
Effects of alcohol
Alcohol changes the way that several neurotransmitters in the brain work.
Neurotransmitters are chemicals that carry neuron signals – Drinking affects neurotransmitters in complex ways. Some effects of drinking alcohol may include:
- memory changes
- loss of inhibition
- changes in emotion, such as increased aggression, sadness, or euphoria
- slowed reflexes
Alcohol can be fatal in high amounts. Like other poisons, the body works to rapidly remove it from the blood, which makes a lot of work for the liver and kidneys.
Over time, excessive alcohol use can cause liver health problems such as cirrhosis. It may also harm the kidneys, heart, and brain. Chronic drinking can even cause dementia by causing a dangerous vitamin B-1 (thiamine) deficiency.
A 2016 study found that very intoxicated people underestimate how drunk they are, how extreme their drinking is, and how likely their drinking is to affect their health.
Its authors explain that people may judge the severity of their intoxication based on how drunk people around them are, which distorts their perceptions in environments where most people are drunk. For example, women and people with more fatty tissue have more rapid increases in BAC. Having a small body size also means that BAC may rise at a quicker pace.
Some other factors that may cause BAC to increase more quickly include:
- how quickly someone drinks
- whether or not a person drinks on an empty stomach
- the strength of the drink a person consumes
- whether or not a person uses other drugs, including some prescription drugs
- how fast a person’s body metabolizes alcohol
For most people, a single drink — for example, 1.5 ounces (oz) of hard liquor, 12 oz of beer, or 5 oz of wine — will elevate blood alcohol by 0.06 or 0.07 per drink.
This means that consuming four to five alcohol drinks in a short amount of time may be enough to put a person at risk of alcohol poisoning, or even death. A single drink may put a person over their state’s BAC limit for driving.
Alcohol tolerance can affect the extent to which a person feels intoxicated. People who frequently drink may feel less drunk than those who do not. People with alcohol use disorder may not feel drunk at all, even when their BAC is very high.
