BACKGROUND: There is concern that increasingly common use of patient assistance programs (PAPs), out-of-pocket assistance provided by manufacturers or foundations, distorts our understanding of patient behavior and insurance design incentives. Yet the current literature on prescription drug cost sharing largely overlooks their use. PAPs prevalence and impact on drug demand and price elasticity is a major knowledge gap. OBJECTIVE: To examine the use of PAPs among patients with multiple sclerosis (MS) and the association with drug demand in a specialty pharmacy program within a regional integrated health system that facilitates their use. METHODS: We used pharmaceutical claims data from December 2017 to December 2018 linked to detailed payer information from Kaiser Permanente Washington to characterize the prevalence of PAPs for users of 7 MS specialty drug molecules. We estimated price elasticity of demand (PED) in a two-part model by using the presence of copayment assistance as a source of cost variation. The first part estimated marginal probability of a claim in a given month with a probit model, comparing PAP users and nonusers, whereas the second part estimated days supplied of a medication, given a claim was made as a measure for demand. RESULTS: Of 789 unique patients, 480 (60.7%) used PAPs in at least 1 drug claim during the 13-month time frame, and 248 patients (31.4%) used PAPs for all of their MS drug claims. When used, copay assistance covered 100% of out-of-pocket (OOP) charges for 98% of claims and reduced patient annual OOP cost by $3,493 on average. People who used PAPs had much higher OOP charges, a lower Charlson comorbidity score, and were more likely to have insurance through an exchange. The OOP costs charged to patients was higher for claims where patient assistance was used than claims where assistance was not used ($294 vs $42, P < 0.001). Total claim amount was higher for claims that used assistance ($6,169) than claims that did not ($5,503, P < 0.001). The probability of a patient having a drug claim in a given month was 1.9% higher among those using patient assistance, although this finding was not significant (P = 0.258). An average change in price of -$168.21 with PAP use led to an average change in demand of -0.05 days, for an overall price elasticity of demand (SD = 0.028, P = 0.852) given PAP use of 0.005, indicating that the presence of PAPs did not significantly affect demand. PED estimates were not statistically significant by drug, and the exclusion of Medicare patients did not change this interpretation. CONCLUSIONS: In a mid-size integrated health system in the state of Washington, a program that promotes adherence to specialty drugs via facilitated PAP use was found to reduce patient OOP costs but had no effect on prescription drug utilization. Payers may consider embracing PAPs to remove patient financial barriers to necessary medications and use tools other than cost sharing to influence patient consumption of specialty drugs. DISCLOSURES: This manuscript was funded in part through a Pre-Doctoral Fellowship in Health Outcomes from the PhRMA Foundation awarded to Brouwer for the completion of her dissertation work. Yeung receives some salary support from Kaiser Permanente. The other authors have nothing to disclose.