A Thesis submitted to The University of Arizona College of Medicine - Phoenix in partial fulfillment of the requirements for the Degree of Doctor of Medicine. / The aim of this study is to conduct a systematic review of the existing evidence on marijuana use and its association, or the absence of an association, with an increased risk of developing chronic obstructive pulmonary disease (COPD), lung cancer, and/or chronic respiratory symptoms. We hypothesize that a systematic review will not demonstrate sufficient evidence to determine that marijuana use increases the risk of developing COPD, lung cancer, and/or chronic respiratory symptoms. The term “chronic respiratory symptoms” encompasses the following: cough, sputum production, wheeze, shortness of breath, acute bronchitis, and chest tightness. The following databases were searched for the topics of marijuana smoking, COPD, lung cancer, and chronic respiratory symptoms: MEDLINE (PubMed/OvidSP), the Cochrane Controlled Trials Register, the Cochrane Database of Systematic Reviews, PsycINFO, the Database of Abstracts of Reviews of Effects, and Google Scholar. The search ended September 7th, 2016. Studies were initially limited only by the requirement that they were based upon human research and published in English. Studies were included if they were systematic reviews, randomized controlled trials (RCTs), prospective or retrospective cohort studies, case control studies, or cross‐sectional studies. A total of 739 articles were screened for eligibility, 17 unique studies met the inclusion criteria and underwent qualitative analysis1‐17. The quality of systematic reviews was evaluated using the AMSTAR criteria18; cohort, case‐control, and cross sectional studies were evaluated based upon the Newcastle‐Ottawa Quality Assessment Scale (NOS) 19. No RCTs were identified. The overall quality of the evidence for each outcome was determined by utilizing the GRADE methodology20‐21. Studies were primarily assessed by a single reviewer, with random validation of assessments on a limited number of studies by a second reviewer. Overall, there is very low quality evidence that assesses for an association between marijuana smoking and an increased risk of developing lung cancer, COPD, and/or chronic respiratory symptoms. There was no conclusive finding for lung cancer and COPD. However, seven of eight studies concluded that there was an association between marijuana use and chronic respiratory symptoms. The totality of evidence describing any associations between marijuana smoking and the risk of developing lung cancer, COPD, and/or chronic respiratory symptoms is not strong enough to confidently state that marijuana use is associated with any of these chronic pulmonary conditions. Of all the evidence examined in this systematic review, the most convincing appears to be that relating to a potential positive association between marijuana smoking and the risk of developing chronic respiratory symptoms. Unfortunately, the overall quality of evidence was very low due to significant methodological weaknesses within the studies. Thus, there is insufficient evidence in the current literature to make a definitive statement regarding this possible association.