Research released by the IAM has revealed that one in ten young male drivers has, at some point, driven a car while under the influence of cannabis.
The shocking statistic comes just after the Government announced it hopes to introduce laws to make drug driving an easier offence to detect and punish.
According to the IAM, figures calculated from the latest annual Think! Road Safety Survey show that 750,000 people have driven under the influence of cannabis, while 370,000 have driven while high on class A drugs.
Introducing effective drug driving laws will not be simple, however, as there's still a debate about whether limits can be set above which it's certain a person is unfit to drive - as is the case with alcohol.
The IAM's Simon Best said: "Any new equipment that will allow police to make quick and accurate decisions at the roadside or at the police station on drivers who are impaired by drugs is great. In this way traffic officers can get back out onto the frontline of roads policing, where their impact is highest.
"But the introduction of a drugalyser type test needs to be backed up by some measure of impairment. Without this, the test could simply catch those people who have used drugs at some point, but are not necessarily still impaired by them."
A new drug driving bill would remove the need for police to prove impairment, and instead give traffic officers equipment that measures chemicals in the body.
Those caught could face a fine up to £5,000, a 12-month driving and a six-month prison sentence.
Road safety charity Brake's Ellen Booth said: "This is an incredibly important step forwards in tackling drug driving which Brake welcomes wholeheartedly. Creating a new offence as well as approving roadside drug screening devices by the end of 2012, will make an enormous difference in preventing drug driving crashes, and also ensuring justice for families whose lives are turned upside down by selfish drug drivers."