Background Social modeling has the capacity to shape treatment outcomes, including side effects. Purpose This study investigated the influence of social modeling of treatment side effects, gender, and participant empathy, on side effects of a placebo treatment. Methods Ninety-six participants (48 females) completed a study purportedly investigating the influence of modafinil (actually placebo) on alertness and fatigue. The participants were randomly seated with a male or female confederate and saw this confederate report experiencing side effects or no side effects. Participant empathy was assessed at baseline. Changes in modeled and general symptoms, and misattribution of symptoms, were assessed during the session and at 24-hr follow-up. Results During the experimental session, seeing side effect modeling significantly increased modeled symptoms (p = .023, d = 0.56) but not general or misattributed symptoms. Regardless of modeling condition, female participants seated with a female model reported significantly more general symptoms during the session. However, response to social modeling did not differ significantly by model or participant gender. At follow-up, the effect of social modeling of side effects had generalized to other symptoms, resulting in significantly higher rates of modeled symptoms (p = .023, d = 0.48), general symptoms (p = .013, d = 0.49), and misattributed symptoms (p = .022, d = 0.50). The experience of modeled symptoms in response to social modeling was predicted by participants' levels of baseline empathy. Conclusions Social modeling of symptoms can increase the side effects following treatment, and this effect appears to generalize to a broader range of symptoms and symptom misattribution over time. Higher baseline empathy seems to increase response to social modeling.