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What are the pulmonary effects of smoking marijuana?
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What are the pulmonary effects of smoking marijuana?
June 01, 2007 | Infection [1]
By Jeanette M. Tetrault, MD [2] and Kristina Crothers, MD [3]
Marijuana is the most commonly used illicit drug in the United States. The prevalence of marijuana
use has remained stable over the past several years, with 14.6 million persons older than 12 years
reporting past-month use in 2005. Given the prevalence of illicit use and interest in the medicinal
use of marijuana, an understanding of the potential negative health consequences of marijuana
smoking is needed. While tobacco smoking is clearly associated with numerous adverse respiratory
complications, including increased cough and wheeze, the development of chronic obstructive
pulmonary disease (COPD), lung cancer, and an increased incidence of infections,1-3 the relationship
between marijuana and pulmonary disease is controversial, despite similarities in many compounds
found in marijuana and tobacco smoke.
Marijuana is the most commonly used illicit drug in the United States. The prevalence of marijuana
use has remained stable over the past several years, with 14.6 million persons older than 12 years
reporting past-month use in 2005. Given the prevalence of illicit use and interest in the medicinal
use of marijuana, an understanding of the potential negative health consequences of marijuana
smoking is needed. While tobacco smoking is clearly associated with numerous adverse respiratory
complications, including increased cough and wheeze, the development of chronic obstructive
pulmonary disease (COPD), lung cancer, and an increased incidence of infections,1-3 the relationship
between marijuana and pulmonary disease is controversial, despite similarities in many compounds
found in marijuana and tobacco smoke.
Evidence supports that smoking marijuana is significantly associated with increased respiratory
symptoms. In a recent systematic review of the literature,4 we found that in 14 of 14 articles that
focused on this issue, the incidence of respiratory complications was substantially higher for
marijuana users than for nonsmokers of marijuana. Symptoms and signs included cough, phlegm,
dyspnea, hoarse voice, pharyngitis, and bronchi- tis. Notably, cough, phlegm, and wheezing
remained significantly increased in marijuana smokers after controlling for concomitant tobacco use
and other potential confounders in 2 of the higher-quality studies included in our review.5,6
The impact of marijuana on pulmonary function and the development of COPD is less clear from the
literature. One reason for apparently conflicting data may be that marijuana smoking appears to
have potentially different effects on pulmonary function depending on whether testing is done after
short-term exposure or long-term use. Past literature suggested that short-term marijuana smoking
has a bronchodilating effect. In our systematic review,4 we confirmed the bronchodilating effect of
short-term exposure to marijuana in 11 of 12 experimental studies.
However, the data regarding the long-term effects of marijuana use have been conflicting. Despite
the association with cough, phlegm, and wheezing, we found that long-term marijuana smoking has
not been associated with measures of airflow obstruction or other abnormalities in pulmonary
function. In 3 observational cohort studies,6-8 no clear association was found between marijuana
smoking and longitudinal decline in the forced expiratory volume in 1 second.
The association of marijuana smoking with lung cancer also has been controversial. In another
systematic review,9 we assessed 19 articles and found that marijuana smoking was associated with
premalignant changes in the lung that included many cytomorphological changes, such as
metaplasia, alveolar macrophage tumoricidal dysfunction, and oxidative stress.
In addition, all of the 4 studies that measured tar exposure showed increased tar retention in the
lungs of marijuana smokers compared with tobacco-only smokers; the association between tar
deposition in the lung and the development of lung cancer has been established.10 Despite the
association between marijuana smoking and changes at a cellular level, studies have failed to
demonstrate an increased risk of lung cancer in marijuana smokers when controlling for tobacco
smoking.
Several reports suggested an association between marijuana smoking and pulmonary infections in
both immunocompromised and immunocompetent persons. Some of the risk for infection may be
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What are the pulmonary effects of smoking marijuana?
Published on Patient Care Online (http://www.patientcareonline.com)
related to behaviors associated with sharing of marijuana smoke, such as "shotgunning" or
"hotboxing," as opposed to exposure to infectious agents within the marijuana itself. Pulmonary
infections in marijuana smokers have included pneumonias11 and tuberculosis.12 In addition,
marijuana smokers may have increased exposure and sensitivity to Aspergillus and other fungal
pathogens.13,14
Finally, marijuana smoking also may be associated with barotrauma. Smoking marijuana differs from
tobacco smoking in that marijuana smokers have a larger puff volume, greater depth of inhalation,
and longer breath-holding time. Several reports describe pneumomediastinum and pneumothorax in
marijuana smokers.15
Overall, these reviews have led us to conclude that marijuana and tobacco smoking share some
negative pulmonary consequences; however, there are some distinct differences. Barotrauma that is
seen with marijuana smoking is not generally seen with tobacco smoking and likely results from the
differences in smoking dynamics. In addition, with short-term exposure to marijuana smoke, there
seems to be an association with bronchodilation that is not seen with tobacco smoking. Both
marijuana and tobacco smoking cause cytomorphological changes in the lungs and symptoms of
cough, phlegm, and wheezing. Yet despite clear biological plausibility, a direct association between
marijuana smoking and the development of lung cancer or COPD has not been determined.
A final answer to the question "how does smoking marijuana compare with tobacco smoking in terms
of its effects on the lungs?" will not be available until we have carefully designed longitudinal studies
that compare the effects of tobacco and marijuana smoking on lung health. As noted in our
systematic reviews, prior studies have been of varying quality in the degree to which they have
adjusted for tobacco smoking and other confounders and in how they have measured exposures and
outcomes. For example, studies have not adjusted for occupational or environmental exposures.
Thus, future studies will not only need to account for potential confounding factors but will also need
to define standard exposure and outcome criteria to accurately assess potential associations.
References: 1. Health consequences of smoking: A report of the Surgeon General [Atlan- ta, Ga]:
Department of Health and Human Services, Centers for Disease Control and Prevention, National
Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health;
Washington, DC: USGPO, 2004. Available at: http://www.cdc.gov/
tobacco/data_statistics/sgr/sgr_2004/ index.htm. Accessed March 14, 2007. 2. Pauwels RA, Rabe KF.
Burden and clinical features of chronic obstructive pulmonary disease (COPD). Lancet.
2004;364:613-620.3. Weiss W. Cigarette smoking and lung cancer trends: a light at the end of the
tunnel? Chest. 1997;111:1414-1416. 4. Tetrault JM, Crothers K, Moore BA, et al. Effects of marijuana
smoking on pulmonary function and respiratory complications: a systematic review. Arch Intern Med.
2007;167:221-228. 5. Moore BA, Augustson EM, Moser RP, Budney AJ. Respiratory effects of
marijuana and tobacco use in a US sample. J Gen Intern Med. 2005;20:33-37.6. Sherrill DL,
Krzyzanowski M, Bloom JW, Lebowitz MD. Respiratory effects of non-tobacco cigarettes: a
longitudinal study in general population. Int J Epidemiol. 1991;20:132-137.7. Tashkin DP, Simmons
MS, Sherrill DL, Coulson AH. Heavy habitual marijuana smoking does not cause an accelerated
decline in FEV1 with age. Am J Respir Crit Care Med. 1997;155:141-148.8. Taylor DR, Fergusson DM,
Milne BJ, et al. A longitudinal study of the effects of tobacco and cannabis exposure on lung function
in young adults. Addiction. 2002; 97:1055-1061.9. Mehra R, Moore BA, Crothers K, et al. The
association between marijuana smoking and lung cancer: a systematic review. Arch Intern Med.
2006;166:1359-1367.10. Zang EA, Wynder EL. Cumulative tar exposure. A new index for estimating
lung cancer risk among cigarette smokers. Cancer. 1992;70:69-76. 11. Park DR, Sherbin VL,
Goodman MS, et al; Harborview CAP Study Group. The etiology of community-acquired pneumonia at
an urban public hospital: influence of human immunodeficiency virus infection and initial severity of
illness. J Infect Dis. 2001;184:268-277.12. Oeltmann JE, Oren E, Haddad MB, et al. Tuberculosis
outbreak in marijuana users, Seattle, Washington, 2004. Emerg Infect Dis. 2006;12:1156-1159.13.
Denning DW, Follansbee SE, Scolaro M, et al. Pulmonary aspergillosis in the acquired
immunodeficiency syndrome. N Engl J Med. 1991;324:654-662.14. Kagen SL, Kurup VP, Sohnle PG,
Fink JN. Marijuana smoking and fungal sensitization. J Allergy Clin Immunol. 1983;71: 389-393.15.
Fajardo LL. Association of spontaneous pneumomediastinum with substance abuse. West J Med.
1990;152: 301-304.
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What are the pulmonary effects of smoking marijuana?
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Links:
[1] http://www.patientcareonline.com/infection
[2] http://www.patientcareonline.com/authors/jeanette-m-tetrault-md
[3] http://www.patientcareonline.com/authors/kristina-crothers-md
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