Marijuana use leads to difficulty in concentrating and thinking. It also decreases the user ability to memorize things. (1—4). In addition, user’s of marijuana have an increased tendency to ‘remember’ things that did not happen. (5,6) Most marijuana users do not realize that these effects of marijuana on mental ability persist for up to 6 hours after the last use of the drug. The user may not feel high, but his reaction times are slower and memory skills are decreased. These changes can decrease ability in sports, other physical activities, and in studies.

Marijuana may be more detrimental to memory function than is alcohol or cocaine. (7) This effect may be due to the presence of cannabinoid receptor sites (activation of these receptors interrupts normal brain motor and cognitive function) in the areas of the brain which control memory.
(8,9)

The results of a 1992 study of 48 adult male subjects who smoked marijuana then completed standardized, paper—and—pencil tests of educational development and ability, learning, associative processes, abstraction, and psychomotor performance indicate that all capabilities were impaired except abstraction and vocabulary. (10,11)

Referenses:
1. Andreasson S, Allebeck et al. Cannabis and schizophrenia; A longitudinal study of Swedish conscripts. Lancet 1987 Dec 26; :2483—6.
2. Schwartz RH. Heavy marijuana use and recent memory impairment. Psychiatric Annals 2992 Feb;21(2) :80—2.
3. Abood ME, Martin BR. Neurobiology of marijuana abuse. Trends In Pharmacological Sciences 1992 May; 13(5) :201—6.
4. Nahas G, Latour C. The human toxicity of marijuana. Medical Journal Of Australia 1992 Apr 6;156(7) :495-7
5. Pfefferbaum A, Darley CF, Tinklenberg JR, Roth NT, Kopell BS. Marijuana and memory intrusions. J Nerv Ment Dis
1977;l65(6) :381—6.
6. Block RI, Wittenborn JR. Marijuana effects on associative processes. Psychopharmacol 1985;85:426—30.
7. Brown J, Kranzler HR. Delboca FK. Self—reports by alcohol and drug abuse inpatients — factors affecting reliability and validity. British Journal Of Addiction 1992 Jul;87(7) :10]3—24.
8. Matsuda LA, Bonner TI, Lolait SJ. Localization of cannabinoid receptor messenger RNA in rat brain. Journal of Comparative Neurology 1993 Jan 22;327(4) :535—50.
9. Heyser CJ, Hampson RE, Deadwyler SA. Effects of delta—9—tetrahydrocannabinol on delayed match to sample performance in rats — alterations in short—term memory associated with changes in task specific firing of hippocampal cells. Journal Of Pharmacology And Experimental Therapeutics 1993 Jan;264 (1) 294-307.
10. Block RI, Farinpour 1k, Braverman K. Acute effects of marijuana on cognition — relationships to chronic effects and smoking techniques. Pharmacology Biochemistry And Behavior 2992 Nov;43(3) :907—17.
11. Azorlosa JL, Heishman SJ, Stitzer ML, Mahaffey JM. Marijuana smoking — effect of varying delta—9—tetrahydrocannabinol content and number of puffs. Journal Of Pharmacology.

Source:www.cesar.umd.edu/metnet, Nov 1998