There have been emotional scenes in a Penrith court during sentencing submissions for a man who crashed his car while under the influence of drugs, killing three of his friends.

Jordan Brown, 21, has pleaded guilty to dangerous driving causing death and driving under the influence of drugs over the 2015 crash near Bilpin.

He told the hearing he fell asleep while driving home from a dance festival and rolled his car.

Lachlan Burleigh, 17, Ben Sawyer, 19, and Luke Shanahan, 21, died in the crash. All were from Sydney's northern beaches.

The mother of one of the men killed, Georgina Sawyer, told a packed courtroom the grief she was suffering was insurmountable and she was completely broken.

"I have so much hate, it scares me ... I will never recover from this," she said.

Ms Sawyer said she would never forgive the driver.

"That kid [her son Ben] never stood a chance. He was driven to his death," she said.

"I'm not interested in the law or another adjournment. Please give him [Brown] a minimum of 10 years."

'I wish it was me who died'

Brown told court he took one ecstasy capsule about 36 hours before the crash.

"I didn't think the drugs would still be in my system," he said.

Brown was reminded by the judge that a toxicology report indicated a high level of drugs in his system, suggesting he had taken the ecstasy closer to the time of the crash than he was admitting.

He told the court he could not explain the high reading.

"I feel terrible knowing I'm still here," Brown told the court.

"My mates didn't deserve to go that way. I wish it was me who died that day."

Brown, who was a P-plate driver at the time of the crash, was refused bail and will be sentenced later this month.