Just 0.5% of motorists said they had driven under the influence of drugs in 2012/13, official figures show.
This compares with 1% of drivers who admitted the offence during the 2011/12 financial year, a survey by the Office of National Statistics (ONS) shows.
Data also showed that 6.4% of motorists said they had driven under the influence of alcohol at least once in 2012/13, compared with 7.4% the previous year.
People aged between 25 and 29 were shown to be the worst offenders, with 10% admitting drink-driving at least once during 2012/13, up from the 2011/12 figure of 8.6%.
AA president Edmund King said: “It is encouraging to see a significant drop in the number of drivers who say they have driven under the influence of illegal drugs in the last year.
“The problem of drug driving is no secret and it needs to be tackled. It is concerning that young drivers in their twenties were twice as likely (1%) than the general driving population (0.5%) to say they had drug driven in the last year.”
Provisional figures showed that there were 470 road fatalities in Britain last summer – July to September. This was the same figure as summer 2012, while those killed or seriously injured (KSIs) dropped 3% to 6,520.
Meanwhile slight injuries were down 4% to 42,570.
Road casualties down
The ONS figures also showed that total car user and pedestrian casualties were down, but there was a 1% rise in the number of motorcyclist casualties, as well as a an 8% increase in pedal cyclist KSIs.
The Department of Transport said these rises were at least partly due to different weather conditions in summer 2013, as summer 2012 was far wetter than normal.
Total child KSIs were down 15% and child pedestrians KSIs dropped by 17%.
Neil Greig, director of policy and research at the Institute of Advanced Motorists, said the decrease in road accident casualties is reassuring.
He added: “But the fact remains that nearly a quarter of road deaths are a result of criminal driving acts. Targeted action by the police to drive down the numbers of these criminal driving acts could potentially have huge societal benefits.”