Abstract Objectives: We measure for the first time how commercially available Cannabis flower products affect feelings of fatigue. Methods: A total of 1,224 people recorded 3,922 Cannabis flower self-administration sessions between June 6, 2016, and August 7, 2019, using the Releaf App. Usage sessions included real-time subjective changes in fatigue intensity levels prior to and following Cannabis consumption, Cannabis flower characteristics (labeled phenotype, cannabinoid potency levels), combustion method, and any potential experienced side effects. Results: On average, 91.94% of people experienced decreased fatigue following consumption with an average symptom intensity reduction of 3.48 points on a 0–10 visual analog scale (SD = 2.70, d = 1.60, p < 0.001). While labeled plant phenotypes (“C. indica,” “C. sativa,” or “hybrid”) did not...