This study examines state Medicaid programs to determine the effects of the many prescription drug cost containment methods on reimbursement expense.  The study provides a wealth of state-data and determined that only tiered-copay was significantly associated with lower prescription cost.  The authors note limitations of their study design and recommend further research. 

Kelton, C. M., Rebelein, R. P., Heaton, P. C., Ferrand, Y., & Guo, J. J. (2008). Differences in the cost of antidepressants across state Medicaid programs. Journal of Mental Health Policy and Economics, 11(1): 33-47.  http://www.icmpe.org/test1/journal/issues/v11i1/v11i1abs05.html

Authors: Christina M. Kelton, Robert P. Rebelien, Pamela C. Heaton, Yann Ferrand, Jeff J. Guo