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Cannabis (Marijuana)
by Erowid
Use of cannabis is relatively safe, compared to many recreational psychoactives. There are no confirmed deaths caused by cannabis alone, although deaths can and do result from injuries sustained while intoxicated. Especially when combined with alcohol, cannabis has been shown to reduce driving ability and can contribute to traffic accidents. The primary health concerns related to cannabis use are lung and airway health (but not cancer), accidental injuries, reversible reductions in memory scores, and triggering of paranoid and psychotic thinking in vulnerable individuals.

It is worth noting that the first large age cohort (people who were in their teens between 1967 and 1980) of heavy, frequent cannabis smokers in the United States is only now reaching the age at which many serious health complications occur.

For many years, anti-cannabis campaigns have included the theory that the use of cannabis causally leads to use and abuse of other recreational psychoactives. This "Gateway Theory" is now considered a debunked myth, with dozens of scientific papers showing that other factors cause the correlation and cannabis use itself does not cause the use of other drugs. Even the DEA has abandoned this theory.1,2,3,4

The political climate around cannabis and other recreational psychoactive substances makes it complicated to find balanced opinions about its safety and risks. Prohibitionist organizations and individuals are more likely to emphasize risks associated with heavy use and those who believe cannabis should be legalized focus on the much lower risks associated with occasional use.5

Cannabis use does not, by itself, cause death. Deaths can result from accidental injuries (such as car accidents). Extreme panic reactions, especially after oral consumption of high dose cannabis, have resulted in many people being briefly hospitalized until they come down, but no deaths from anxiety reactions have been reported.

  • Dramatic Changes in Thinking. Changes to thought processes, while among the primary reasons why people choose to use cannabis, can also impair judgement.
  • Respiratory Ailments. Frequent smoking of cannabis can lead to respiratory ailments, including COPD, associated with smoke inhalation. The most common negative health impact of regular cannabis smoking are lung and throat problems including: coughing, increased frequency of throat and lung infections, and reduced lung capacity.

    Although cannabis smokers have used bongs/water pipes to reduce the impact on their lungs, a 1995 study6 suggests that use of water pipe does not lower the overall ratio of particulate matter to THC and may be counterproductive. In other words, it lowers the particulate matter, but it also lowers the amount of THC, and may cause users to simply smoke more material. Vaporizers are reported to reduce the lung impact of 'smoking' cannabis.

    A large, well-designed study of tens of thousands of hospital patients found that cannabis use does not cause cancers of the airway and lungs.7,8,9,10
    In 2013, a comprehensive review of all studies on regular use of cannabis and lung health and found that although regular cannabis use was associated with airway irritation and increased bronchitis, it is not associated with with the development of lung cancer, chronic obstructive pulmonary disease (COPD), emphysema, or bullous lung disease. The author, Donald Tashkin writes:
    "[H]abitual use of marijuana alone does not appear to lead to significant abnormalities in lung function [...] [F]indings from a limited number of well-designed epidemiological studies do not suggest an increased risk of either lung or upper airway cancer from light or moderate use. Overall, the risks of pulmonary complications of regular use of marijuana appear to be relatively small and far lower than those of tobacco smoking." (Tashkin 2013) 13
  • Short-Term Memory Impairment. Cannabis intoxication is known to cause memory impairment during the period of acute effects, but the reduced ability to store and recall memories can linger for days and affect cognitive or academic test scores.
  • Panic and Anxiety Attacks. Some people may experience panic attacks (including extreme feelings of dread, accelerated heart rate, feeling as if they're going to die) from smoking cannabis. [See the Psychedelic Crisis FAQ for information about such an occurrence.]
  • Increased Heart Rate. Cannabis use causes an increase in heart rate in many users, usually lasting for the period of intoxication and slowing back down as the cognitive effects wane.
  • Cannabis and Mental Health. Cannabis use has been implicated in triggering psychosis and other mental health problems. Although these issues are complex and (as of 2015) still an active area of research, a 2011 report by the FDA in their role as US Department of Health and Human Services advisors to the DEA found no clear causal linkage between cannabis use and psychotic mental disorders.10,11,12
  • Cannabis and Brain Area Shrinkage In the 2000s, a new risk was suggested by some researchers that using cannabis by teenagers could cause reductions in the volumes/sizes of certain important brain areas. These were not experimental studies, but instead used brain scans of living humans. Research published in 2015 by Weiland et al. found no differences in those brain areas in a tightly controlled study.
  • Cannabis and Intelligence / IQ Loss (mostly myth) In 2016, it appears that the National Insitute on Drug Abuse is finally beginning to admit that cannabis does not cause reductions in IQ and does not damage intelligence directly. There has been persistent evidence that heavy cannabis use during the teens was associated with lower performance on some academic or intelligence tests, but no studies were able to actually demonstrate a causal link. A paper in 2016 by Jackson et al. using matched twins and studied over a decade demonstrated that no causal hypothesis fit the data. But what the research does seem to suggest is that heavy use of cannabis during high school can reduce interest in performing well in school and thus is associated with lower scores on tests such as increased vocabulary.15
  • Cannabis Interactions. Cannabis is not known to have negative health interactions with many other drugs, but some report unpleasant effects when combined with alcohol or venlafaxine (Effexor). See Venlafaxine Interactions.

  • Medical Uses. Cannabis has many possible medical uses. Symptom relief is claimed for ailments such as cancer, AIDS wasting syndrome, and glaucoma. Patients have found that the appetite-stimulating and anti-nausea properties of cannabis can help to mitigate the drastic weight loss and weakness from wasting syndrome and the nausea of cancer chemotherapy, and help them to regain weight. Cannabis reportedly helps glaucoma patients by reducing ocular pressure, which can cause damage to the eye.

    Cannabis and cannabinoids have repeatedly been found to be effective at treating chronic pain, neuropathic pain, and spacicity associated with multiple sclerosis. (Hill K, 2015)

    For more information about the medical use of cannabis, visit the
    Medical Marijuana Vault.
References #
  1. Federal Register. "'Marijuana as a "Gateway Drug' in 'Denial of Petition To Initiate Proceedings To Reschedule Marijuana; Proposed Rule'". Jul 2011(76)131.
  2. Golub A, Johnson BD. "The Misuse of the 'Gateway Theory' in U.S. Policy on Drug Abuse Control: A Secondary Analysis of the Muddled Deduction". International Journal of Drug Policy. Jun 2002;13(1),5-19.
  3. Zimmer L, Morgan JP. "Exposing Marijuana Myths: A Review of the Scientific Evidence - Claim #13 Marijuana is a 'Gateway' to the Use of Other Drugs". Lindesmith Center 1995.
  4. Van Gundy K, Rebellon CJ. "A Life-course Perspective on the 'Gateway Hypothesis'". J Health Soc Behav. 2010 Sep 14;51(3):244-59.
  5. Hall W. "Appraisals of the Adverse Health Effects of Cannabis Use: Ideology and Evidence". FAS Drug Policy Analysis Bulletin. Jun 1999(7).
  6. Gieringer D. "Marijuana Water Pipe and Vaporizer Study". MAPS Newsletter. Summer 1996(6)3.
  7. Hashibe M, Morgenstern H, Cui Y, et al. "Marijuana use and the risk of lung and upper aerodigestive tract cancers: results of a population-based case-control study". Cancer Epidemiol Biomarkers Prev. 2006 Oct;15(10):1829-34.
  8. Kaufman M. "Study Finds No Cancer-Marijuana Connection". Washington Post, May 26 2006.
  9. Biello D. "Large Study Finds No Link between Marijuana and Lung Cancer". Scientific American. May 24 2006.
  10. Erowid E. "Cannabis & Psychosis : a guide to current research about cannabis and mental health". Erowid Extracts. Jun 2005;8:4-7.
  11. Erowid E. "Cannabis & Psychosis : Additional Notes and References". Jun 1 2005.
  12. Federal Register. "Denial of Petition To Initiate Proceedings To Reschedule Marijuana; Proposed Rule". Jul 2011(76)131.
  13. Tashkin DP. "Effects of marijuana smoking on the lung" Ann Am Thorac Soc. 2013 Jun 27;10(3):239-47.
  14. Debunking the Latest Pathetic Fear Smear Campaign Against Marijuana: No, smoking pot likely will not make you psychotic.. Alternet. Feb 22, 2015
  15. Jackson NJ, Isen JD, Khoddam R, Irons D, Tuvblad C, Iacono WG, McGue M, Raine A, Baker LA. "Impact of adolescent marijuana use on intelligence: Results from two longitudinal twin studies" Proc Natl Acad Sci U S A. 2016 Feb 03;113(5):E500-8.
Revision History #