Pharmaceutical patient assistance programs (PAPs) have the potential to improve prescription drug accessibility for eligible patients, but currently there is limited information regarding their effectiveness. In an attempt to provide a systematic description of primary studies on PAPs, we reviewed 33 unique studies from commercial and grey literature (e.g., government publications, conference abstracts) sources: 15 health care outcome evaluations, seven economic evaluations, seven surveys and four miscellaneous studies. Enrollment assistance for PAPs with additional medication services (e.g., counseling) was significantly associated with improved glycemic (standardized mean difference=-0.40, 95% CI=-0.59,-0.20; k=3 one-group, pre-post-test; 1 comparison-group) and lipid (standardized mean difference=-0.52, 95% CI=0.78,-0.27; k=3 one-group, pre-post-test; 1 comparison group) control. Inadequately designed economic evaluations suggest free PAP medications offset health care institutions' costs for uncompensated medications and enrollment assistance programs. More rigorous research is needed to establish the clinical and cost-effectiveness of PAPs from a patient and health care institution perspective.