'Intoxication' May Not Always Be Visible

"It is important to understand and recognize intoxication because of the risk for injury that results from it," said John Brick, lead author and executive director of Intoxikon International. "Understanding and recognizing an intoxicated person can help us make decisions about allowing a person to drive, accepting a ride from someone, or cutting off a drinker."

Key points of the review include:

• "Obvious intoxication" as defined in some courts is not always the same as "visible intoxication."

"While most people would use these terms interchangeably to mean that someone was clearly drunk," said Brick, "laws in some states differentiate between the terms. For example, in some states 'obvious' intoxication means that if someone has consumed a large number of drinks, it should be obvious that they are intoxicated and not capable of driving. Other state laws define 'visible' intoxication as specific types of behavior, such as trouble walking, slurred speech and other common signs of alcohol intoxication. Thus, it is possible to have a unique legal situation where someone is obviously intoxicated, but not visibly intoxicated based on specific legal definitions."

In most people reliable signs of intoxication are present by casual observation at a blood alcohol concentration (BAC) of 150 mg/dl or more, even in most tolerant individuals. At a BAC of less than 150 mg/dl, signs of visible intoxication are not reliably present in most drinkers, and the likelihood of identifying signs of impairment is less than chance.

"This presents a particular challenge to preventionists," said Brick. "For example, how do you intervene or make an informed decision about driving with someone if they do not appear visibly intoxicated? People who are too impaired to drive are not typically staggering, slurring their speech, or presenting gross signs of intoxication."

Unfortunately, there is no easy way to determine how someone can reach a BAC of 150 mg/dl, he added.

"A very small woman drinking rapidly could attain a BAC of 150 mg/dl with only four standard drinks, whereas a large man might require 10 or 12 such drinks, again depending on how long they were drinking and other scientific factors," he said. "While these analyses can be calculated scientifically based on specific individuals and circumstances, for general purposes it may be better to focus on observable signs of intoxication."

Drink counting can be a useful prevention approach in some cases.

In situations where exceptionally tolerant individuals do not show signs of visible intoxication even though they are very intoxicated, the only way to know if they are intoxicated might be to count drinks, Brick explained.

"Although helpful in some cases, this is not without difficulty because you do not know how much the person consumed before they started drinking at your restaurant or party," said Brick. "Also, if you have a policy that allows a certain number of drinks per hour, for example, you may rely on counting rather than paying attention to behavior, and end up overserving. Drink counting is also problematic in a busy bar, restaurant, or social gathering … and drink sizes can vary widely." He said there is a need for further research to establish a reasonable maximum number of drinks to be served, coupled with training to identify signs of intoxication.

"Our review is important for scientists, law enforcement and the legal community, and particularly everyday people," said Brick. "We want readers to know that just because someone who has been drinking does not look visibly intoxicated it does not mean they are not impaired to drive. Similarly, if after drinking someone is showing one or more signs of visible intoxication such decreased inhibitions, doing or saying things they would not if sober, or psychomotor impairment, showing trouble walking, standing, or slurred speech, or cognitive impairment, as in easily confused, or impaired memory, judgment and mental tasks, then that person is probably well above the legal definition of intoxication in the US and probably has a BAC in excess of 150 mg/dl. Their risk for a serious accident is also very high."

While prevention efforts have become more sensitive to drinking and driving, he said, establishing "intoxication" has also become more dependent on special tests, such as those used by police, and not available to the general public. "Ultimately," he said, "if there is uncertainty as to whether someone is intoxicated, it is better to err on the side of caution, terminate service, and arrange for alternate transportation."