Adam Roy Triffett, 28, pleaded guilty this week to two counts of causing grievous bodily harm by dangerous driving at Hillwood on October 13, 2012.

That night Triffett set out from Rocherlea to George Town in a 1999 green Holden Commodore to buy morphine.

Despite receiving a speeding ticket earlier that day, Triffett drove at 180km/h, three times the speed limit, along George Town Road, the Supreme Court in Launceston heard.

Passengers including Ricky Damien Brown, Lisa Maree Butler and Mark Leigh Freeman repeatedly asked Triffett to slow down as he hit 200km/h on the East Tamar Highway.

Several cars were overtaken.

"It knocked my car off course a bit," one motorist told police.

"I thought the car was going to crash for sure the way it was driving."

Another driver said Triffett almost ran into her before illegally overtaking in a right-hand turning lane.

Crown prosecutor Virginia Jones said drivers who saw Triffett that night were convinced he would crash.

As Triffett entered a sweeping left-hand bend at 160km/h, his car left the road.

Ms Butler, who was not wearing a seatbelt, told investigators that it felt like being inside a washing machine as the car rolled.

She suffered a collapsed lung and vertebrae along with an injured shoulder.

Mr Brown, also not wearing a seatbelt, said he could not recall how many times the car rolled but thought he was going to die, the court heard.

He was flung from the vehicle and when he saw Triffett's car come to a stop about 20 metres away, he thought everyone in it was dead, Ms Jones told the court.

Mr Freeman, who was wearing a seatbelt, suffered a severe cut to the head and an injured femur.

At the time of the crash Triffett was under the influence of methylamphetamine and cannabis, the court heard.

Defence counsel Evan Hughes said his client's plea of guilty was a reflection of his remorse.

Justice Robert Pearce adjourned the matter for sentencing later this month.