Rationale: Prior research shows decreased brain volume in regular cannabis users. However, not much is known about the effect of low-dose, recreational cannabis use during adolescence.

Method: Researchers compared brains, IQ, and behavior in two groups of young people: one group who just used cannabis once or twice by age 14 and another group who had never used the drug.

Results: 14-year-olds who had only used cannabis 1-2 times had higher brain volume than subjects with no cannabis use. The change in users was associated with impaired cognition and a greater likelihood of developing anxiety.

Meaning: These data suggest that even very little cannabis use in adolescence leads to structural brain changes, decreased cognitive performance, and higher risk of anxiety.