Marijuana, Cannabis Sativa, has been used for centuries for its medicinal and euphorant properties, and its fibers, to make hemp cloth and paper. Medicinally, between 1850 and 1942, it was prescribed in the United States Pharmacopeia as a remedy for a variety of ailments including gout, tetanus, depression, and cramps (Farthing 1992). Today, it is used for reducing intraocular pressure due to glaucoma, as an antiemetic to relieve nausea associated with chemotherapy, and as an appetite stimulant for AIDS patients. Recreationally, it is the most widely used illicit drug, especially among adolescents.
The main psychoactive component of marijuana is (9-tetrahydrocannabinol (THC). Other prominent cannabinoids include cannabidiol, cannabinol, and (9-tetrahydrocannabinic acid. Together, these compounds contribute to various behavioral and cognitive changes, which can slightly differ based on the route of preparation and administration (Farthing 1992). THC is found in the sticky resin of the cannabis plant, with the highest concentration in the flowering tops (buds) of the female plant. Marijuana is a preparation of the leaves, stems, and buds, while hash is a concentration of the resin. Smoking and oral ingestion are the most common ways of administration and can produce slightly distinct effects due to the different filtering methods of the digestive tract and lungs.
The subjective experience of marijuana can include prolongation of the passing of time, altered awareness of self and the environment, and occasional paranoia or increased anxiety. At high enough doses, hallucinations can also be experienced (Farthing 1992). While intoxicated, a large range of acute cognitive effects has been found, including difficulty in motor coordination and impairment of learning, attention, and memory (Murray 1985).
Although there are a large number of studies and evidence showing the acute effects of marijuana on memory, studies on the long-term effects on memory is sparse. In this paper, my objective is to determine potential chronic effects of marijuana on memory. I do this by selectively reviewing studies on this topic and attempt to integrate the findings, which range from neurobiological standpoints to more general effects on cognitive behavior.
In earlier attempts of finding the cannabinoid receptor, using THC as the ligand proved difficult because of its lipid solubility which cause non-specific, high affinity binding. In Herkenham et al. (1990), they localize cannabinoid receptors (CB1) throughout the brain by using synthesized, radiolabeled CP 55,940, structurally similar to THC, but less hydrophobic and more potent as a cannabinoid receptor ligand. They find high density binding in the cerebellum and basal ganglia (which regulates time perception and coordinated movement), the cerebral cortex (perception and reasoning) and the hippocampus, which is associated with memory. This correlates with marijuana's distortion of these cognitive...