Christian Calderwood had to be forced to a halt by other drivers who surrounded him with their vehicles and then took his keys.
Stirling Sheriff Court was told that Calderwood (42), of Townhead, Kirkintilloch, appeared to be almost unconscious behind the wheel of his Vauxhall Astra and was foaming at the mouth and barely able to stand by the time police arrived to help.
The court heard he was first spotted driving erratically on the M80 west of Stirling at about 5pm one Monday last May, at the start of the evening rush, and was speeding up and slowing down and veering from lane to lane.
Lindsey Brooks, prosecuting, said that other motorists were so concerned about the way he was driving that they began to follow him, and saw that he then joined M9, heading north.
About 5.30pm, a trucker on the M9 who was doing about 55 miles per hour in the inside lane watched in horror in his mirror as Calderwood’s Astra came up behind him, almost hit him, then overtook, just missing the rear of the lorry, before drifting onto the hard shoulder and back again onto the motorway.
As they passed junction 10, for Stirling and Callander, the lorry driver saw the Astra drift into the acceleration lane meant for traffic joining the motorway, and assumed the driver must be unwell and was pulling up, but then it drifted back onto the main carriageway.
Mrs Brooks said: “All this time the car seemed to be speeding up and slowing down erratically.”
The concerned trucker then decided he would try to bring the car to a halt, and about 150 feet before Keir Roundabout at the Perthshire end of the motorway he slowed to a halt, forcing the Astra to stop behind him, while motorists in cars stopped alongside him, “effectively blocking him in”.
One witness took the keys out of the Astra’s ignition.
Mrs Brooks, the depute fiscal, said: “The witnesses spoke to the accused, who seemed to be confused and foaming from the mouth.”
Calderwood staggered out and went to his boot, saying he was looking for his keys.
Police, called by other drivers, arrived after a few minutes and found Calderwood still standing at the boot.
Mrs Brooks said: “The police noted he was unsteady on his feet, unaware of his surroundings, where he was, or what he was doing.
“There appeared to be white powder round his mouth and the officers said they were having difficulty keeping him awake.”
He was told to take a roadside breath-test, but did not appear to understand what he was being asked to do.
Mrs Brooks said: “The police couldn’t smell alcohol, and formed the opinion he was impaired by some other drug.”
He was arrested and taken to Falkirk Police Station, where a police surgeon confirmed the officers’ opinion and took a blood test which, on analysis, showed high levels of a drug called Etizolam.
The drug, prescribed for insomnia and anxiety by Japanese and Indian doctors in carefully-controlled doses, is abused in the west and known as “e-tizzy” for its “unsubtle” effects.
It is described on one website as “a black out ride down a highway to coma”.
Calderwood, single and unemployed, pleaded guilty to driving while unfit through drugs in the incident on May 23 last year.
Defence agent Peter Farrell said it had been the first time that Calderwood had taken Etizolam, and shortly after he had done so he had got a call from his girlfriend who was staying in a caravan somewhere near Stirling and wanted him to come and collect her.
Mr Farrell said: “When he left Glasgow he thought that he’d be all right.”
Sheriff Wyllie Robertson, who heard that Calderwood was not suitable to carry out unpaid work, placed him under social work supervision for 18 months under a community payback order and banned him from driving for two years.