Cannabis use for symptom management among patients with cancer has increased significantly in recent years, with many reporting benefits for pain, anxiety, sleep, nausea, appetite as well as other symptoms. However, rigorous prospective data on the potential benefits and harms of cannabis use in this population are lacking. This Commentary describes a United States National Cancer Institute (NCI)-led initiative addressing this research gap by supporting five prospective observational studies evaluating the benefits and harms of cannabis use among a large, heterogeneous samples of patients with cancer undergoing active systemic treatment. We provide an overview of each study, including cancer type, treatment modalities, inclusion/exclusion criteria, data collection methods, and both patient-reported and cancer-related outcomes. Published by Oxford University Press 2026.