Human groups make up for themselves, for the others and for the events they live explanations that, although not scientific, determine the practices that regulate their behavior. In the case of marijuana consumption, the representations of young people in particular and society in general influence the decision about whether or not to continue consuming. The perception of risk associated with consumption by high school students dropped from 60% in 1994 to 36.9% in 2004, which backs up the relationship between high consumption and low risk perception. Cannabis is the illegal drug with the highest indexes of consumption in the world with an increasing growth rate, to which we may add the alarming reduction in the age when people begin consuming it. This research paper is concerned with the effects of consumption on cognitive processes in school and social performance: a drop in performance, more problems getting along with others, absenteeism and drop out. The study aims to know how low marihuana doses affect cognitive ability in post-primary students. There are no studies concerned with the effect of marihuana in non-patient students (i.e. not diagnosed with addictive behavior and not considered socially as drug addicts). Material and methods Sample: The sample comes from high school students in public schools, private subsidized schools and private paying schools. The sample was stratified by non-proportional affixation, considering the sex, course and social economic level variables, and was made up of 304 students in high schools of the Metropolitan Area (Santiago), belonging to low, medium, and high socioeconomic groups (determined by dependence and the city in which the school is located). The research is descriptive, not experimental, ex post facto. Instruments: Group application to the entire sample (n=304) a) Psychosocial evaluation and consumption questionnaire, abbreviated and adapted, aimed at the collection of demographic data, consumption behaviors and other required information. The young people are identified with a number in order to ensure their anonymity and thus promote the truth of the responses. b) Domino Test (D-48): Evaluates non-verbal intelligence. It controls differences caused by social and educative factors. It is applied on a group basis in order to discard subjects whose IQ is lower than average, regardless of consumption. Individual application to the consumer group and the non-consumer group. a) Rey Complex Figure Test: Widely used in recent studies on the effects of drugs on teenagers. Evaluates neuropsychological functioning. b) Benton Test: Evaluates current intellectual efficiency from the attention span, concentration and immediate retention. c) Verbal memory (Rey): Evaluates immediate verbal memory. Results General: The total results for the three schools polled and evaluated show that 14.5% of the students declared that they consumed marijuana at least four times during the last month. The proportion in the three establishments is not distributed in a homogenous fashion, but is concentrated in the low social economic level school (27.8%), with the lowest percentage in the high social economic level school. With regard to sex, 11% are girls and 15.7% are boys. Although a higher proportion of the boys consumed, the consumption in girls shows a sustained increase in recent years. A significant group is beginning to consume marijuana at age 15 or even earlier. The perception of risk associated with frequent consumption and the possibility of quitting smoking on a voluntary basis show significant differences: among consumers (C), 51% consider that there is no risk or negative effect in consumption, while only 10% of nonconsumers (NC) share this perception. Protective factors or those associated with risk The family.… [ABSTRACT FROM AUTHOR]