Association Between Marijuana Use and Risk of Cancer

This systematic review and meta-analysis assesses the association of marijuana use with the development of cancer in adults with at least 1 joint-year exposure (equivalent to 1 joint per day for 1 year).


Observational studies: criteria based on the Newcastle-Ottawa scale
Representativeness of the exposed cohort 1 = truly representative of the average patient in the community 1 = somewhat representative of the average patient in the community 0 = selected group of users (e.g., nurses, volunteers) 0 = no description of the derivation of the cohort Selection of the non-exposed cohort Enter 0 or 1: 1 = drawn from the same community as the exposed cohort 0 = drawn from a different source 0 = no description of the derivation of the non-exposed cohort Ascertainment of exposure Enter 0 or 1: 1 = biological test (e.g., blood/urine) 1 = structured interview 1 = written self-report that characterizes dose (current or cumulative) 0 = written self-report without quantification of exposure 0 = no description

Clinical Trials: Criteria based on the Cochrane risk of bias tool
Domain Support for judgement Random sequence generation Describe the method used to generate the allocation sequence in sufficient detail to allow an assessment of whether it should produce comparable groups. Allocation concealment Describe the method used to conceal the allocation sequence in sufficient detail to determine whether intervention allocations could have been foreseen in advance of, or during, enrolment. Blinding of participants and personnel. Assessments should be made for each main outcome (or class of outcomes).
Describe all measures used, if any, to blind study participants and personnel from knowledge of which intervention a participant received. Provide any information relating to whether the intended blinding was effective. Blinding of outcome assessment. Assessments should be made for each main outcome (or class of outcomes).
Describe all measures used, if any, to blind outcome assessors from knowledge of which intervention a participant received. Provide any information relating to whether the intended blinding was effective. Incomplete outcome data. Assessments should be made for each main outcome (or class of outcomes).
Describe the completeness of outcome data for each main outcome, including attrition and exclusions from the analysis. State whether attrition and exclusions were reported, the numbers in each intervention group (compared with total randomized participants), reasons for attrition/exclusions where reported, and any reinclusions in analyses performed by the review authors. Representativeness of the exposed cohort  (12), and weekly or more frequent use (52) and also complete a physical examination.
1 -Participants filled a questionnaire on ever versus never use of marijuana in lifetime, and lifetime frequency of marijuana use. Users were categorized based on lifetime marijuana use as: never (reference group), once, 2-4 times, 5-10 times, 11-50 times, and more than 50 times (a category defined as ''heavy'' use).
1 -Participants filled a questionnaire on the number of times of cannabis use (none, 1 or 2 times, 3-10 times, 11-99 times, 100-499 times, or >500 times). Cannabis users were characterized as non-use or any use.

Han et al, 2010 (32) (cross-sectional)
Representativeness of the exposed cohort 1 -Participants filled a questionnaire on if they were current marijuana smokers (smoking currently and more than six times ever), former marijuana smokers (denial of current smoking but admission to having smoked more than six times ever), or nonsmokers (never smoking) 1 -Duration of use of any illicit drugs was measured from the earliest age at initiation to the latest age at last use of any illicit drug (never used, < 1 year, 2-10 years, or 11 years or more). 1 -Matched to cases on age (± 3 years), gender, and town of residence. Results were adjusted for age and gender, covariates such as race, education, HPV16 serology, family history of cancer, smoking pack-years, and average alcohol drinks per week.

Ascertainment of exposure done prospectively or retrospectively
1 -Unclear comparability of cases and controls based on the design/analysis (matched for ± 5 years age and district health boards). Results were adjusted for age, pack-years of cigarette smoking, sex, ethnicity, family history of lung cancer.
1 -Adjusted within studies for age, sex, race, education, and tobacco smoking (never vs. ever) and packyears of tobacco.