The purpose of this study is to determine the feasibility and the effects of cannabis with high concentrations of CBD in patients receiving chemoradiation for GBM. This is not a therapeutic study for the treatment of glioblastoma. Patients will first complete a cannabis sampling session to assess for initial marijuana tolerability. Proceeding this, patients will complete 3-5 outpatient smoking sessions per week over a 6 week period. During each session, patients will be given 90 minutes to smoke 0.5 to 2 cannabis cigarettes. Outcome measures will include measures of pain, mood, nausea, quality of life, and the both the potentially positive and negative subjective effects of cannabis. Food intake, opioid use, and compliance to cannabis treatment will be investigated. It is hypothesized that concurrent use of cannabis with chemoradiation in the treatment of patients with GBM will be feasible, well tolerated and may decrease radiation-induced toxicities.