The combination of alcohol and caffeine produces a potentially lethal mix that just makes it harder to realise you are actually drunk in the first place. And the study published in Behavioural Neuroscience suggests popular caffeinated energy drinks could also raise risks from intoxication rather than lessen them.
In laboratory tests caffeine made mice more alert but did not reverse the awareness problems caused by alcohol, including their ability to avoid things they should have known could hurt them.
Dr Thomas Gould, of Temple University, Philadelphia, said: “The myth about coffee’s sobering powers is particularly important to debunk because the co-use of caffeine and alcohol could actually lead to poor decisions with disastrous outcomes.
“People who have consumed only alcohol, who feel tired and intoxicated, may be more likely to acknowledge that they are drunk.
“Conversely, people who have consumed both alcohol and caffeine may feel awake and competent enough to handle potentially harmful situations, such as driving while intoxicated or placing themselves in dangerous social situations.”
Dr Gould and colleagues investigated how alcohol, caffeine or a combination of both affected the ability of mice to negotiate a maze and learn to avoid unpleasant stimuli.
Mice given alcohol alone were found to be less anxious, moved around more but had problems learning to avoid the unpleasant stimuli.
Those given the equivalent of up to six to eight cups of coffee for humans were more anxious, moved around less and learned less well.
If given both alcohol and caffeine, the alcohol was found to block the caffeine’s ability to make the mice anxious, but did not reverse the alcohol’s effect to inhibit learning. As a result, alcohol calmed the caffeine jitters, leaving the animal more relaxed but less able to avoid threats.
In people, this combination could lead to them thinking they are only slightly drunk and able to function normally – such as drive a car – when in fact, they are unable to do so.
Dr Gould said: “The alcohol-energy drink combinations have skyrocketed in popularity.”
He cited other evidence that these drinks produce deficits in general cognitive ability and raise the odds of alcohol-related problems such as drunken-driving citations, sexual misconduct, and needing medical assistance.
He added: “The bottom line is that, despite the appeal of being able to stay up all night and drink, all evidence points to serious risks associated with caffeine-alcohol combinations.”
The US Food and Drug Administration is looking into the safety and legality of combination alcohol-caffeine beverages. In November, it sent letters to 30 manufacturers asking for evidence that such drinks are safe and legal under FDA regulations.
To date, the FDA has only approved caffeine as an additive in soft drinks at concentrations less than 200 parts per million and has not approved adding caffeine at any level to alcoholic beverages.
Under the Federal Food, Drug and Cosmetic Act, a substance added intentionally to food such as caffeine in alcoholic beverages is deemed unsafe and is unlawful unless its particular use has been approved by FDA regulation or is generally recognised as safe.