Twelve long-term marihuana users were studied after smoking natural marihuana, synthetic δ9-transtetrahydrocannabinol (δ9-THC), and placebo cigarettes. The subjective, cognitive, and physiologic changes tended to be greater for marihuana than for δ9-THC, although the syndromes produced were very similar. There was also a marked placebo effect on subjective measures that is suggestive of the importance of learning in the marihuana subjective syndrome. The apparent deficit in memory produced by marihuana appeared to be due to an attentional decrement rather than one of longer-term information storage. Reaction time, both unrewarded and with a monetary incentive, was unaffected by the drugs.
Galanter M, Weingartner H, Vaughan TB, Roth WT, Wyatt RJ. δ9-Transtetrahydrocannabinol and Natural MarihuanaA Controlled Comparison. Arch Gen Psychiatry. 1973;28(2):278-281. doi:10.1001/archpsyc.1973.01750320106016