Matthew Huron examining a marijuana plant in his grow house.
Credit: Ed Andriesk/AP

A large study conducted in the United Kingdom failed to find evidence of a robust link between cannabis use and lowered intelligence among teenagers.

The study, published online January 6 in the Journal of Psychopharmacology, found a statistical association between cannabis use and decreased intellectual performance. However, this association vanished when the researchers took other variables into account. “The notion that cannabis use itself is causally related to lower IQ and poorer educational performance was not supported in this large teenage sample,” wrote Claire Mokrysz of the University College London and her colleagues.

The findings are based on 2,235 teenagers who participated in the Avon Longitudinal Study of Parents and Children (ALSPAC), a long-term study following children born in the Bristol area in 1991 and 1992. The children had their IQ tested at the age of 8, and again at the age of 15. Nearly a quarter of the participants […]