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Effects of Heavy Marijuana Use on Learning and Social Behavior

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Heavy Marijuana use has been shown to effect a person's developement in many ways.

Depression(1), anxiety(2), and personality disturbances(3) have been associated with marijuana use. Research clearly demonstrates that marijuana has potential to cause problems in daily life or make a person’s existing problems worse. Because marijuana compromises the ability to learn and remember information, the more a person uses marijuana the more he or she is likely to fall behind in accumulating intellectual, job, or social skills.  Moreover, research has shown that marijuana’s adverse impact on memory and learning can last for days or weeks after the acute effects of the Drug wear off(4, 5).

Students who smoke marijuana get lower grades and are less likely to graduate from high school, compared with their non-smoking peers(6, 7, 8, 9). A study of 129 college students found that, for heavy users of marijuana (those who smoked the drug at least 27 of the preceding 30 days), critical skills related to attention, memory, and learning were significantly impaired even after they had not used the drug for at least 24 hours(10). The heavy marijuana users in the study had more trouble sustaining and shifting their attention and in registering, organizing, and using information than did the study participants who had used marijuana no more than 3 of the previous 30 days. As a result, someone who smokes marijuana every day may be functioning at a reduced intellectual level all of the time.

More recently, the same researchers showed that the ability of a group of long-term heavy marijuana users to recall words from a list remained impaired for a week after quitting, but returned to normal within 4 weeks(11). Thus, it is possible that some cognitive abilities may be restored in individuals who quit smoking marijuana, even after long-term heavy use.

Workers who smoke marijuana are more likely than their coworkers to have problems on the job. Several studies associate workers’ marijuana smoking with increased absences, tardiness, accidents, workers’ compensation claims, and job turnover. A study of municipal workers found that those who used marijuana on or off the job reported more “Withdrawal behaviors”—such as leaving work without permission, daydreaming, spending work time on personal matters, and shirking tasks—that adversely affect productivity and morale(12). In another study, marijuana users reported that use of the drug impaired several important measures of life achievement including cognitive abilities, career status, social life, and physical and mental health(13).

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Definitions of Terms Used

Addiction Strong physiological, emotional and/or psychological dependence on a substance such as alcohol or drugs that has progressed beyond voluntary control. For more on addiction see the section Addiction Information in this website. 
Cannabis The botanical name for the plant from which marijuana comes. 
Chronic Refers to a disease or condition that persists over a long period of time. Also a slang term for a particularly potent strain of marijuana. 
Drug Any substance, other than food, that changes the function or structure of the body or mind when ingested. Drugs essentially are poisons. The degree they are taken determines the effect. A small amount acts as a stimulant. A greater amount acts as a sedative. A larger amount acts as a poison and can kill one dead. This is true of any drug. Each has a different amount at which it gives those results. 
Marijuana A psychoactive drug made from the leaves of the cannabis plant. It is usually smoked but can also be eaten. See Cannabis. 
Withdrawal Symptoms that occur after chronic use of a drug is reduced or stopped. 

  1. Brook JS, et al: The effect of early marijuana use on later anxiety and depressive symptoms. NYS Psychologist, January 2001, pp. 35-39.

  3. Green BE, Ritter C: Marijuana use and depression. J Health Soc Behav 41(1):40-49, 2000.

  5. Brook JS, Cohen P, Brook DW: Longitudinal study of co-occurring psychiatric disorders and substance use. J Acad Child and Adolescent Psych 37:322-330, 1998.

  7. Pope HG, Yurgelun-Todd D: The residual cognitive effects of heavy marijuana use in college students. JAMA 272(7):521-527, 1996.

  9. Block RI, Ghoneim MM: Effects of Chronic marijuana use on human cognition. Psychopharmacology 100(1-2):219-228, 1993.

  11. Lynskey M, Hall W: The effects of adolescent Cannabis use on educational attainment: a review. Addiction 95(11):1621-1630, 2000.

  13. Kandel DB, Davies M: High school students who use crack and other drugs. Arch Gen Psychiatry 53(1):71-80, 1996.

  15. Rob M, Reynolds I, Finlayson PF: Adolescent marijuana use: risk factors and implications. Aust NZ J Psychiatry 24(1):45-56, 1990.

  17. Brook JS, Balka EB, Whiteman M: The risks for late adolescence of early adolescent marijuana use. Am J Public Health 89(10):1549-1554, 1999.

  19. Ibid ref 22.

  21. Pope, Gruber, Hudson, et al: Neuropsychological performance in long-term cannabis users. Archives of General Psychiatry.

  23. Lehman WE, Simpson DD: Employee substance abuse and on-the-job behaviors. Journal of Applied Psychology 77(3):309-321, 1992.

  25. Gruber, AJ, Pope HG, Hudson HI, Yurgelun-Todd D: Attributes of long-term heavy cannabis users: A case control study. Psychological Medicine 33:1415-1422, 2003.


Source:  National Institute on Drug Abuse


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