Patients with cancer are increasingly using cannabis. This multifaceted botanical, which includes the cannabinoids delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD), shows promise in alleviating symptoms associated with cancer and its treatment. Cannabis, particularly THC, has been approved as an anti-emetic and may be useful in chemotherapy-induced peripheral neuropathy. Less robust data supports using cannabis for insomnia, appetite, and cancer-related non-neuropathic pain. CBD alone does not provide symptom relief for patients with advanced cancer. Some patients are using cannabis to treat their cancer despite the lack of evidence. Cannabis may interact with prescribed medications; generally, these interactions are seen with high orally dosed cannabis. Studies are ongoing to determine the nature of the interaction between cannabis and immunotherapy. Cannabis is generally well-tolerated, with common dose-dependent side effects including dizziness, dry mouth, and psychoactive effects (feeling high, euphoria, disorientation). Patients with active psychiatric or cardiovascular disease should use cannabis products only if monitored closely by a knowledgeable clinician.