Persistent cannabis use that starts in adolescence linked to IQ decline

Tuesday 28th August 2012

Persistent cannabis users who started using the drug before age 18 show an average IQ decline of 8 points and other signs of impaired mental functioning by age 38, according to world-first research emerging from the University of Otago’s long-running Dunedin Multidisciplinary Study.

The Study has followed the progress of 1000 Dunedin-born people since their birth in 1972/73 and is one of the most detailed studies of human health and development ever undertaken. The latest findings are newly published in a paper appearing in the US journal PNAS Plus co-authored by researchers from Otago, Duke University and King’s College London.


Meier, M. H., Caspi, A., Ambler, A., Harrington, H. L., Houts, R., Keefe, R., McDonald, K., Ward, A., Poulton, R., and Moffitt, T. E. Persistent Cannabis Users Show Neuropsychological Decline from Childhood to Midlife. PNAS (Proceedings of the National Academy of Sciences of the USA) , 2012, 109(40): E2657-64. RO624