Even one glass of vodka or wine may hit you hard enough to make you a dangerous driver if you are aged 55 or older.
Researchers from the University of Florida tested how alcohol affects the driving skills of two age groups - 36 people aged between 25-35 and 36 people aged between 55-70.
They found that although neither age groups imbibed enough alcohol to put them over the legal driving limit, just one drink can affect the driving abilities of older drivers.
"Earlier studies looked at how alcohol affects the driving in younger adults but no one has ever looked at the combination of ageing drivers and alcohol," said Sara Jo Nixon, a professor in the department of psychiatry and psychology at the University of Florida, US.
Researchers assessed the older drivers' ability to stay in the centre of their lane and maintain a constant speed. They also looked at how rapidly they adjusted their steering wheel.
For the older drivers, the small, legal levels of intoxication did affect their driving, said the study published in the journal Psychopharmacology.