Researchers at McLean Hospital say that smoking marijuana during adolescence is likely to affect brain functioning.

“We have to understand that the developing brain is not the same as the adult brain,” said Dr. Staci A. Gruber, the paper’s senior author and director of the cognitive and clinical neuroimaging section of the neuroimaging center at McLean, a Harvard-affiliated hospital in Belmont, Massachusetts.

Researchers took 35 chronic cases for study; most of them were just about 22 years old. About 20 of them started smoking before 16, while 15 of them started smoking at or after the age of 16.

Researchers tried to analyze the brain process that was answerable for any kind of nonfigurative thinking. Participants were asked to sort cards; after which researchers observed the ability of their brains to remain focused and observe the rules strictly. They noted that those who started smoking earlier scored lesser than the rest.

At 15, Dr. Gruber said, the brain is still altering, and “the part that modulates executive function is the last part to develop.”

Researchers also noted that those who used marijuana regularly tended to smoke twice as much as the others. The early smokers were noted to have been smoking 14.7 grams per week, almost thrice as much as the rest.

The drive to legalize marijuana in many States should have age-wise restrictions, she said.