Henry Thomas had cannabis in his vehicle when he was busted for a DUI, which could explain him being zonked at the wheel ... this according to law enforcement.
As we reported ... Elliott from 'E.T.' was arrested last month in Oregon after the Tualatin PD responded to a call of him being asleep in the driver's seat at an intersection in a residential area.
According to new court docs ... the responding officer arrived right after another driver had pounded on Thomas' window to wake him up, and noticed he had spit on his now-open window and it was running down the door. He allegedly also had spit on his jacket.
The cop claims she asked Thomas if he was having a medical issue and he said no, but he was slurring his speech and had droopy and bloodshot eyes. According to the docs, he said he didn't have anything to drink, but refused the field sobriety tests.
The officer claims Thomas was swaying as she talked to him so she placed him under arrest for DUI ... and located a bottle of "fast acting THC" in the driver's side door.
The Washington County Oregon Circuit Court clerk tells us ... Thomas' attorney pled not guilty on his behalf Friday to the misdemeanor charge of driving under the influence. He has another court date scheduled for later this month.
We reached out to the attorney ... no word back, so far.