The role of pharmacy experience and argument types in forming beliefs about pharmacist trustworthiness was studied. Study participants were recruited from three primary care clinics. They were provided a pharmacy scenario that contained information that could be used to form causal and authoritative arguments. The participants rated the trustworthiness of the pharmacist in the scenario on a 10-point, Likert-type scale and provided the arguments used to form the trustworthiness belief. Information that contradicted the pharmacist's trustworthiness was then presented in the form of an addendum, and the participants reassessed the pharmacist's trustworthiness. Participants rated the pharmacist using a Likert-type scale. Responses were coded and analyzed. Initial trustworthiness and post-trustworthiness scores were calculated. Participants' pharmacy experience score was also determined. Reliability and principal components analyses were conducted to determine the quality of the trustworthiness and pharmacy experience scores. A total of 130 patients participated in the study. There was a positive correlation between pharmacy experience and the number of causal arguments that subjects used to form their beliefs about pharmacist trustworthiness (r = 0.223, p = 0.012). Results of t tests revealed that belief strength was similar among subjects using more causal than authoritative arguments to form beliefs and in those using fewer causal arguments (t = 1.35, p = 0.179), but belief tenacity differed significantly between the groups (t = -2.303, p = 0.023). The role of external sources in influencing the formation of beliefs about trustworthiness of a pharmacist may be limited as a patient gains pharmacy experience, as experience is based on causal associations. Moreover, causal arguments are correlated with belief tenacity.