Pooled Analysis From North Africa Found Cannabis Smoking Linked to 2.4-Fold Higher Lung Cancer Risk | Research

The takeaway

In a pooled analysis of 430 lung cancer cases and 778 controls from three North African countries, cannabis smoking was associated with a 2.4 times higher lung cancer risk even after adjusting for tobacco.

Read this if you smoke cannabis and want to understand the available evidence on lung cancer risk.

2.4x lung cancer risk for cannabis smokers; 18.2x when combined with tobacco

What the researchers found

Researchers pooled data from three hospital-based studies in Tunisia, Morocco, and Algeria, regions with high cannabis consumption.

Among 430 male lung cancer cases, 15.3% had ever smoked cannabis, compared to 5% of 778 controls. After adjusting for age, country, tobacco smoking, and occupational exposure, the odds ratio for lung cancer among cannabis smokers was 2.4 (95% CI: 1.6-3.8).

The association remained after adjusting for lifetime tobacco pack-years (OR=2.3, 95% CI: 1.5-3.6). Among current tobacco smokers, the combination of tobacco plus cannabis carried an OR of 18.2 compared to 10.9 for tobacco smoking alone.

Lung cancer risk increased with joint-years (cumulative exposure) but not with the dose or duration of cannabis smoking independently, suggesting total lifetime exposure matters most.

Why it matters

While the relationship between cannabis smoking and lung cancer has been debated, this pooled analysis from a high-prevalence region found a significant association even after careful tobacco adjustment. The combined effect of tobacco plus cannabis was notably higher than tobacco alone.

The numbers in context

430 cases, 778 controls. 15.3% of cases vs. 5% of controls ever smoked cannabis. Adjusted OR for cannabis smoking: 2.4 (95% CI: 1.6-3.8). Tobacco-only OR: 10.9. Tobacco + cannabis OR: 18.2. Risk increased with joint-years of cannabis exposure.

How the study worked

Pooled analysis of three hospital-based case-control studies in Tunisia, Morocco, and Algeria. 430 male lung cancer cases and 778 male controls. Logistic regression adjusted for country, age, tobacco smoking (pack-years), and occupational exposure.

What this study cannot tell us

All cannabis smokers were also tobacco users, making it difficult to fully separate the effects. Residual confounding by tobacco despite statistical adjustment is possible. The Maghreb smoking style (often mixing cannabis with tobacco) may differ from other regions. Self-reported cannabis use may be underreported. Hospital-based controls may not represent the general population.

How to read the evidence

This is a pooled analysis of three case-control studies with reasonable sample size and appropriate statistical adjustments, providing moderate evidence, though residual confounding by tobacco remains possible.

When this study was published

Published in 2008. Subsequent large studies (including the 2006 Hashibe cohort study) have produced conflicting results on cannabis-lung cancer associations, and the question remains unsettled.

The bigger picture

This was one of the larger studies specifically examining cannabis and lung cancer at the time. The finding of an independent association after tobacco adjustment, and the multiplicative effect of combined use, contributed to the ongoing debate about cannabis inhalation risks.

Questions still open

Would vaporized or non-smoked cannabis show the same lung cancer association? Is the carcinogenic risk from cannabis, tobacco, or their combination? Would populations with lower tobacco co-use show different results?

Common questions

Does cannabis cause lung cancer?

This study found a significant association between cannabis smoking and lung cancer risk, even after accounting for tobacco. However, the inability to fully separate cannabis and tobacco effects, and conflicting results from other studies, mean the question isn't definitively answered.

Is vaping cannabis safer than smoking it?

This study only examined smoked cannabis. Vaporization avoids combustion and its carcinogenic byproducts, which theoretically could reduce respiratory risks, but long-term vaping safety data is still limited.

Read the original research

Cannabis smoking and risk of lung cancer in men: a pooled analysis of three studies in Maghreb.

Journal of thoracic oncology : official publication of the International Association for the Study of Lung Cancer, 3(12), 1398-403

View on PubMed ↗Publisher’s paper ↗

Citation

Berthiller, Julien; Straif, Kurt; Boniol, Mathieu; Voirin, Nicolas; Benhaïm-Luzon, Veronique; Ayoub, Wided Ben; Dari, Iman; Laouamri, Slimane; Hamdi-Cherif, Mokhtar; Bartal, Mohamed; Ayed, Fahrat Ben; Sasco, Annie J. (2008). Cannabis smoking and risk of lung cancer in men: a pooled analysis of three studies in Maghreb.. Journal of thoracic oncology : official publication of the International Association for the Study of Lung Cancer, 3(12), 1398-403. https://doi.org/10.1097/JTO.0b013e31818ddcde