IQ before and after cannabis use: is it sufficient?

Persistence of regular cannabis use	N	% male	Age 7–13 y full-scale IQ	Age 38 y full-scale IQ	Δ IQ effect size*
Never used	242	38.84	99.84 (14.39)	100.64 (15.25)	0.05
Used, never regularly	508	50.59	102.27 (13.59)	101.24 (14.81)	−0.07
Used regularly at 1 wave	47	72.34	101.42 (14.41)	98.45 (14.89)	−0.20
Used regularly at 2 waves	36	63.89	95.28 (10.74)	93.26 (11.44)	−0.13
Used regularly at 3+ waves	41	78.05	96.00 (16.06)	90.77 (13.88)	−0.35

http://www.pnas.org/content/109/40/E2657/1/T6.expansion.html