Potheads Really Are Slackers, Says Science Their brains have less of motivational chemical dopamine: study By Matt Cantor, Newser User Posted Jul 2, 2013 6:11 AM CDT Updated Jul 7, 2013 9:58 AM CDT 195 comments Comments This Oct. 26, 2010 file photo shows a marijuana plant flourishing under grow lights at a warehouse in Denver. (AP Photo/Ed Andrieski, File) (Newser) – Smoke a lot of marijuana for a long period, and your brain may end up making less of a chemical that helps you stay motivated, scientists say. They researched 19 regular pot smokers and 19 non-smokers of matched age and sex, scanning subjects' brains to see how chemicals were distributed, LiveScience reports. All the users had begun smoking as teens, and an examination of a part of the brain called the striatum revealed lower dopamine levels as compared to their peers. The finding came as a surprise: Users also all reported having had symptoms of psychosis, such as strange thoughts or paranoia. Boosted dopamine has been tied to psychosis symptoms, so researchers had actually expected higher dopamine among weed smokers, LiveScience notes. As for the slacker theory, it remains "controversial," says the lead researcher. One detail worth noting: Past studies involving past or occasional marijuana users didn't come to the same dopamine conclusion, indicating that the production dip isn't necessarily permanent.