Cannabis has been legalized, decriminalized, or medicalized in over half the U.S. states. With restrictions on cannabis research, accepted standards to guide clinical practice are lacking. Analyzing online communications through a digital health platform, we characterized patient questions about cannabis use and provider responses. Coded for content were 4579 questions posted anonymously online between March 2011 through January 2017, and the responses from 1439 U.S. licensed clinicians. Provider responses to medical cannabis use questions were coded for sentiment: "negative", "positive", and "mixed." Responses could be "thanked" by patients and receive "agrees" from providers. The most frequent themes were detection of cannabis use (25.3%), health harms (19.9%), co-use with other substances (9.1%), and medical use (8.2%). The 425 medical cannabis use questions most frequently related to treatment of mental illness (20.3%), pain (20.0%), and cancer care (6.7%). The 762 provider responses regarding medical cannabis use were coded for sentiment as 59.6% negative, 28.6% mixed, and 11.8% positive. Provider sentiment was most positive regarding cannabis use for palliative care and most negative for treating respiratory conditions, poor appetite, and mental illness. The proportion of positive sentiment responses increased from 17.6% to 32.4%. Provider responses coded as negative sentiment received more provider "Agrees" (mean rank = 280) than those coded as positive (mean rank = 215), beta coefficient = 0.33; 95% CI: 0.05, 0.62; p = .02. Cannabis use is a health topic of public interest. Variability in provider responses reflects the need for more research and consensus building to inform evidence-based clinical guidelines for cannabis use in medicine.