Smoking cannabis is an independent risk factor for lung disease in people with HIV

Frequent cannabis smoking is a risk factor for lung disease in HIV-positive men, according to US research published in EClinicalMedicine. Smoking cannabis increased the risk of pulmonary diseases – especially those with an infectious cause – independent of smoking and CD4 cell count. The research involved approximately 2500 men who have sex with men (MSM), half of whom were HIV positive. No independent associations were detected between smoking cannabis and lung disease in HIV-negative men, showing that HIV-positive individuals are especially vulnerable to lung disease caused by smoking the drug.

“To our knowledge, this study is the largest investigation of smoked marijuana [cannabis] and pulmonary diagnoses in HIV infected individuals to date,” comment the authors. “Current daily or weekly marijuana smoking was associated with elevated risk of infectious pulmonary diagnoses in HIV+ participants….current marijuana smoking was also associated with increased risk of chronic bronchitis.”

The authors believe their findings are of relevance to the care of people with HIV and that addressing smoked cannabis use could help reduce rates of pulmonary disease.



Affecting the lungs.


chronic obstructive pulmonary disease (COPD)

Chronic obstructive pulmonary disease (COPD) is a chronic inflammatory lung disease that causes obstructed airflow from the lungs. Symptoms include difficulty breathing, cough, mucus (sputum) production and wheezing. It is caused by long-term exposure to irritating gases or particulate matter, most often from tobacco smoking (active or passive).

equivalence trial

A clinical trial which aims to demonstrate that a new treatment is no better or worse than an existing treatment. While the two drugs may have similar results in terms of virological response, the new drug may have fewer side-effects, be cheaper or have other advantages. 


Any lung infection that causes inflammation. The infecting organism may be bacteria (such as Streptococcus pneumoniae), a virus (such as influenza), a fungus (such as Pneumocystis pneumonia or PCP) or something else. The disease is sometimes characterised by where the infection was acquired: in the community, in hospital or in a nursing home.

It is well known that people with HIV have an increased risk of lung disease. This is partly because of the high rates of smoking among HIV-positive individuals. However, the damage caused by HIV infection and immune suppression are also important causes.

Research involving HIV-negative people has shown that smoking cannabis is a risk factor for respiratory symptoms such as cough and wheezing, as well as chronic obstructive pulmonary disease (COPD) and emphysema. However, relatively little is known about cannabis smoking as a risk factor for pulmonary disease in people with HIV. 

Investigators form the ongoing Multicenter AIDS Cohort Study (MACS) therefore designed a study comparing incidence of infectious lung diseases (such as pneumonia) and non-infectious pulmonary disease, especially bronchitis, between HIV-positive and HIV-negative gay and other MSM, after taking into account smoking of cannabis. Analyses also considered other risk factors for lung disease, especially tobacco smoking, and for people with HIV, CD4 cell count.

The study population consisted of 2704 men aged 30 years and older. Half were HIV positive. Participants were recruited between 1996 (the year combination antiretroviral therapy (ART) was first introduced) and 2014. The average duration of follow-up was a little over ten years. Participants were asked about the frequency and intensity of smoking of cannabis and tobacco, as well as lung disease diagnoses (the latter were also verified using medical records).

The participants had a median age of 44 years and over two-thirds were white. The majority (90%) of HIV-positive people were taking ART and 60% had a CD4 cell count above 350 cells/mm3.

Weekly or daily cannabis smoking lasting at least one year was reported by 27% of HIV-positive individuals and by 18% of HIV-negative individuals. Median duration of daily/weekly cannabis smoking was approximately four years for both groups.

A history of smoking tobacco was a little more common among individuals with HIV compared to those who were HIV negative (65% vs 61%).

Rates of lung disease due to infectious causes were significantly higher among HIV-positive people than HIV-negative study participants (33% vs 22%).

The same was also true for non-infectious lung disease (21% vs 17%).

Closer analysis showed that in people with HIV, rates of both infectious and non-infectious lung disease were markedly higher among cannabis smokers than non-cannabis smokers (41% vs 30%; 25% vs 19%). This finding was not replicated in the HIV-negative group (24% vs 21%; 15% vs 18%).

In HIV-positive participants, the strongest risk factor for diagnosis with a pulmonary infection was a CD4 cell count below 200 cells/mm3 (aHR =3.37; 95% CI, 2.58-4.41, p < 0.001). Current daily or weekly cannabis smoking was also a significant risk factor (aHR = 1.34; 95% CI, 1.06-1.71, p = 0.016).

After taking into account CD4 cell count and smoking status, recent daily or current cannabis use increased the risk of diagnosis with an infectious lung disease by 48% (aHR = 1.48; CI: 1.05-1.75, p = 0.035) with long-term use over two years increasing the risk by 10% (CI: 1.04-1.16, p = 0.012). These risks were amplified by tobacco smoking.

No association was found between smoking cannabis and infectious pulmonary disease among the HIV-negative participants.

Turning to non-infectious lung disease, though both low CD4 cell count and cigarette smoking were stronger risk factors, current cannabis smoking was also a risk factor for the development of chronic bronchitis among men with HIV (HR = 1.54; 95% CI, 1.11-2.13, p = 0.0093). There was no significant association between smoking cannabis and non-infectious pulmonary disease in HIV-negative individuals.

“These findings confirm the known association between HIV infection and increased prevalence of pulmonary disease, and provide evidence that HIV-infected individuals may be more vulnerable to marijuana’s effects on lung disease compared to uninfected participants with similar exposures,” note the authors.

The effect of daily or weekly cannabis smoking on infectious lung disease risk among people with HIV was equivalent to that associated with smoking ten cigarettes daily.

“Marijuana smoking is a modifiable risk factor that healthcare providers should consider when seeking to prevent or treat lung disease in people infected with HIV, particularly those with other known risk factors,” conclude the authors. “Given increased trends of regular marijuana smoking among HIV-infected people…more studies are needed to evaluate potential merits of non-smoked rather than smoked forms of marijuana for medicinal and other purposes.”


Lorenz DR et al. Effect of marijuana smoking on pulmonary disease in HIV-infected and uninfected men: a longitudinal cohort study. EClinicalMedicine,