With two states now legalizing recreational pot, and more to follow, recent opinion polls show the public thinks that pot is less dangerous to your health than sugar, according to a recent Wall Street Journal poll. A new study of those 18 to 25 challenges this fast-forming conventional wisdom.

Randye Hoder at Time summarizes the results of the new study by researchers at Northwestern and Harvard: "The scientists examined two key parts of the brain — the nucleus accumbens and the amygdala, which together help control whether people judge things to be rewarding or aversive and, in turn, whether they experience pleasure or pain from them," Hoder wrote.

"It is the development of these regions of the brain," Hoder reports, "that allow young people to expand their horizons, helping them to appreciate and enjoy new foods, music, books, and relationships."

“This is a part of the brain that you absolutely never ever want to touch,” Hans Breiter, the studies coauthor, told Hoder. “I don’t want to say that these are magical parts of the brain — they are all important. But these are fundamental in terms of what people find pleasurable in the world and assessing that against the bad things.”

"Breiter and his colleagues found that among all 20 casual marijuana smokers in their study — even the seven who smoked just one joint per week — the nucleus accumbens and amygdala showed changes in density, volume, and shape. The scientists also discovered that the more pot the young people smoked, the greater the abnormalities," Hoder reported.

Staci Gruber, an associate professor of psychiatry at Harvard Medical School, told USA Today this week that the new results rang true to her research.

"There have been a growing number of studies that suggest that marijuana use in emerging adults is associated with differences in brain structure and cognitive abilities," Gruber said. "I'm not saying (pot smoking) is analogous to shooting heroin or cocaine, but it's also not quite the benign substance people thought it was."

This is only the latest health warning to come from the scientific community even as public opinion races the other direction.

In February, Francis Collins, director of the National Institutes of Health, told USA Today that it is already known that regular use by adolescents lowers IQ by about 10 points, with lifelong impact. "Perhaps it would be better if, before we plunged into this, there was a little bit more recognition of that particular consequence," Collins said.

Email: eschulzke@desnews.com