BACKGROUND: News stories represent an important source of information. We aimed to evaluate the impact of "spin" (i.e., misrepresentation of study results) in health news stories reporting studies of pharmacologic treatments on patients'/caregivers' interpretation of treatment benefit. METHODS: We conducted three two-arm, parallel-group, Internet-based randomized trials (RCTs) comparing the interpretation of news stories reported with or without spin. Each RCT considered news stories reporting a different type of study: (1) pre-clinical study, (2) phase I/II non-RCT, and (3) phase III/IV RCT. For each type of study, we identified news stories reported with spin that had earned mention in the press. Two versions of the news stories were used: the version with spin and a version rewritten without spin. Participants were patients/caregivers involved in Inspire, a large online community of more than one million patients/caregivers. The primary outcome was participants' interpretation assessed by one specific question "What do you think is the probability that 'treatment X' would be beneficial to patients?" (scale, 0 [very unlikely] to 10 [very likely]). RESULTS: For each RCT, 300 participants were randomly assigned to assess a news story with spin (n = 150) or without spin (n = 150), and 900 participants assessed a news story. Participants were more likely to consider that the treatment would be beneficial to patients when the news story was reported with spin. The mean (SD) score for the primary outcome for abstracts reported with and without spin for pre-clinical studies was 7.5 (2.2) versus 5.8 (2.8) (mean difference [95% CI] 1.7 [1.0-2.3], p < 0.001); for phase I/II non-randomized trials, 7.6 (2.2) versus 5.8 (2.7) (mean difference 1.8 [1.0-2.5], p < 0.001); and for phase III/IV RCTs, 7.2 (2.3) versus 4.9 (2.8) (mean difference 2.3 [1.4-3.2], p < 0.001). CONCLUSIONS: Spin in health news stories reporting studies of pharmacologic treatments affects patients'/caregivers' interpretation. TRIAL REGISTRATION: ClinicalTrials.gov, NCT03094078 , NCT03094104 , NCT03095586.