Alcohol impairs mental performance
Alcohol impairs the functioning of the brain for longer than previously thought, research suggests.
In fact, even after people think the effects have worn off, it is actually still having a negative impact on certain functions.
Scientists examined the effect of alcohol on complex, or executive, brain functions such as abstract reasoning, planning and the ability to monitor our own behaviour in response to external feedback.
They found that performance in these areas was affected even after the concentration of alcohol in the blood had dipped to the point that people were no longer aware of its effect.
In fact, the effect on these "higher order" brain functions appeared to be more pronounced as blood alcohol concentration began to decline from its peak.
Executive brain functions are controlled by an area of the brain known as the frontal lobe.
The frontal lobe is more than twice as large in humans as it is in our nearest primate relatives.
Many scientists believe it is this area of the brain that defines us as a species because it provides us with the ability for complex thought.
The researchers compared the performance of volunteers who were given a mix of alcohol and orange juice to drink with that of a control group who were given a non-alcoholic placebo.
Lead researcher Professor Robert Pihl, of McGill University, Montreal, Canada, said the results had serious implications for activities such as driving.
He said: "People who think they've waited their two hours before driving home may need to actually wait six hours.
"Or else, maybe at the time when you least expect it, you're the most vulnerable."
"The drinker in the process of re-attaining sobriety is likely to be more dangerous, for example, than the drinker who is still imbibing."
A spokeswoman for the charity Alcohol Concern told BBC News Online: "It is obviously a matter of concern that alcohol affects cognitive performance.
"We need to be more aware of the effect of alcohol has on our functioning."
Action on Addiction welcomed the study.
"These results confirm what many have long suspected", said Lesley King-Lewis, its chief executive. "People cannot think clearly after drinking, even the next day."
"This has important economic implications. British office staff have a culture of drinking after work. This research suggests that they cannot be effective the next day.
"Binge-drinking can also have serious effects on mental health. The effects of alcohol on the brain are not yet fully understood and need to be investigated further.
"This research is particularly concerning as more and more people are regularly drinking well over the recommended limits."
The research is published in the journal Alcoholism: Clinical & Experimental Research.