Pulmonary Effects of Marijuana Inhalation

Megan L Howden; Matthew T Naughton


Expert Rev Resp Med. 2011;5(1):87-92. 

In This Article

Literature Review

A literature review was conducted using PubMed and Medline searches for articles related to marijuana use and the associations with respiratory symptoms and disease.

Marijuana is the most commonly used illicit drug worldwide and the second most commonly smoked substance after tobacco.[2] It is derived from the plant Cannabis sativa and is consumed for the psychoactive effects associated with the active substance δ-9-tetrahydrocannabinol (THC).[3] In the USA, 14.6 million people are estimated to be current or recent users of marijuana.[101] Of these people, approximately 20% smoke marijuana on an almost daily basis.[4] In other western countries the figures are similar with an increase in marijuana use over recent decades and subsequent stability.[5] Recent figures suggest approximately 10% of 21-year olds smoke cannabis regularly.[6] Although marijuana can be consumed orally and smoked in a variety of means, life-time cumulative consumption is often measured in 'joint-years' (i.e., one joint daily for 12 months equals one joint-year). This level of consumption tends to decrease as individuals age, one of the reasons for the difficulty in obtaining accurate data about the detrimental effects of marijuana on health.

The gaseous and particulate composition of marijuana and tobacco cigarettes is similar, with the exception of the active components, THC and nicotine.[2] The amount of tar and carcinogens inhaled during marijuana smoking is comparable. However, owing to the techniques commonly used during the smoking of marijuana, there may be greater deposition of these harmful substances in the airways. In particular, marijuana is usually smoked without a filter and burns much hotter (due to a shorter butt) than tobacco cigarettes. In addition, marijuana fumes are often inhaled to maximum inspiration with longer breath holding to increase THC absorption. This may lead to significant variation in the deposition of tar and carbon monoxide, depending on the mode of administration, depth of inspiration and length of breath holding.[7,8]

Histological evidence indicates that marijuana exposure can injure the respiratory epithelium and reduce ciliated epithelial cell numbers, a change almost identical to that seen in tobacco smokers.[4,9] Endobronchial biopsies have also shown evidence of goblet cell metaplasia, reserve cell hyperplasia and squamous cell metaplasia.[9] These and other effects may lead to edema and inflammation of the airways as well as mucus hypersecretion.[10,11]

Unfortunately, it is difficult to accurately study the effects of marijuana on the respiratory system. This is related to the inconsistency in the method of administration between subjects,[7] the illegal nature of the substance leading to problems with nonbiased recruitment, the concurrent use of tobacco in many participants and the often relatively short duration of regular marijuana use compared with tobacco smoking.[12] Nevertheless, it is the opinion of the authors that cannabis smoking has a detrimental effect on the respiratory system in a number of ways, including symptoms, lung function, and possibly carcinogenesis and respiratory tract infections,[13] although the available evidence is conflicting.


There have been a small number of studies that have attempted to examine the effects of marijuana smoking on respiratory symptoms, independent of tobacco smoking. In 1987, Tashkin et al. administered questionnaires to a convenience sample of 144 marijuana smokers and 133 smokers of both marijuana and tobacco.[14] These were compared with control groups of tobacco smokers and nonsmokers. The findings of this early study suggest that regular marijuana smoking results in symptoms similar to that of tobacco smoking with an increased incidence of chronic cough, sputum production, wheeze and episodes of acute bronchitis. These results have been replicated in subsequent longitudinal studies involving random or selected samples of populations in the USA.[4,15] Importantly, significant symptoms were reported with less than one marijuana cigarette smoked per day on average.[15] This suggests that respiratory symptoms can occur with fewer marijuana cigarettes than with tobacco cigarettes. This again may be related to the way marijuana is rolled and smoked. Moore et al. found that marijuana smokers tended to be younger, single males with less income and less education on average.[4] In addition, they reported that while symptoms are similar between marijuana and tobacco smokers, those who smoke marijuana generally develop these symptoms at a younger age. There has also been evidence to suggest that marijuana smokers have a greater utilization of outpatient services for both respiratory conditions and other health problems.[16]


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