Patients' Access to Treatments Act of 2013 - Amends the Public Health Service Act to establish cost-sharing limits for health plans that cover prescription drugs and use a formulary or other tiered cost-sharing structure. Prohibits such a health plan from imposing cost-sharing requirements, including co-payment and co-insurance, applicable to prescription drugs in a specialty drug tier that exceed the dollar amount of cost-sharing requirements applicable to prescription drugs in a non-preferred brand drug tier. Applies the non-preferred brand drug tier for which beneficiary cost-sharing is lowest, if a formulary used by the health plan contains more than one non-preferred brand drug tier.

Defines: (1) "non-preferred brand drug tier" as a category of prescription drugs within a tier in a formulary for which beneficiary cost-sharing is greater than tiers for generic drugs or preferred brand drugs, and that are not included within a specialty drug tier; and (2) "specialty drug tier" as a category of prescription drugs within a tier in a formulary for which beneficiary cost-sharing is greater than tiers for generic drugs, preferred brand drugs, or non-preferred drugs in the plan's formulary.