Including narratives in health-care interventions is increasingly popular. However, narrative information may bias individual's decision making, resulting in patients making poorer decisions. This systematic review synthesises the evidence about the persuasiveness of narrative information on individuals' decision making. Seventeen studies met the review criteria; 41% of studies employed first person narration, 59% third person. Narrative information influenced decision making more than the provision of no additional information and/or statistically based information in approximately a third of the studies (5/17); studies employing first person narratives were twice as likely to find an effect. There was some evidence that narrative information encouraged the use of heuristic rather than systematic processing. However, there was little consistency in the methods employed and the narratives' content to provide evidence on why narratives affect the decision process and outcome, whether narratives facilitate or bias decision making, and/or whether narratives affect the quality of the decision being made. Until evidence is provided on why and how narratives influence decision making, the use of narratives in interventions to facilitate medical decision making should be treated cautiously.