NEW YORK (AP) — A new analysis is challenging the idea that smoking marijuana during adolescence can lead to declines in intelligence.

Instead, the new study says, pot smoking may be merely a symptom of something else that’s really responsible for a brainpower effect seen in some previous research.

Researchers said it’s not clear just what this other factor is.

The study was released Monday by the Proceedings of the National Academy of Sciences. Researchers looked at data previously collected on 3,066 twins who had taken a battery of intelligence tests at ages 9 to 12, and again at ages 17 to 20.

The study tracked how test scores changed, in both marijuana users and abstainers. Analysis suggested that marijuana use itself made no difference.