According to multiple sources, Hopper, 24, was pulled over while driving in Nebraska on Wednesday for failure to signal when an officer suspected drug activity and searched the car.
Troopers found 14g of marijuana, 4 amphetamine pills, and 3g of psilocybin mushrooms, reports E! News.
Along with Hopper, actress Uma von Wittkamp was also in the car at the time.
Hopper Penn and Robin Wright
Hopper was arrested and booked for possession of mushrooms and less than one ounce of marijuana while von Wittkamp was booked for possession of amphetamines and mushrooms, reports TMZ.
Both Hopper and von Wittkamp are in custody at the Hamilton County Jail awaiting bail.
Hopper is the youngest child of Sean and Robin. The former couple also share 26-year-old daughter Dylan Penn.
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Hopper has been open about his struggle with addiction in the past, saying his dad’s tough love helped him get clean.
“I was doing a lot of stuff,” he said, “but meth was the main one that brought me down.”
Hopper Penn and Sean Penn
Hopper eventually agreed to get help, but only after getting a firm ultimatum from his dad.
“I went to rehab because I woke up in a hospital and my dad was like, ‘Rehab? Or bus bench?’ I was like, ‘I’ll take the bed,’ ” he said.