As lower-cost versions of original biologic drugs made by different manufacturers, follow-on biologics offer the promise of meaningful savings for the US health care system and improved patient health outcomes through greater medication adherence. Fulfillment of this promise, however, is predicated on the prescribing of such products. Under state drug product selection laws, pharmacists may substitute prescriptions for brand name, small-molecule drugs with their generic equivalents, but will be indefinitely prohibited from substituting prescriptions for original biologics with their follow-on biologic counterparts given a lack of product-specific guidance on demonstrating interchangeability. Even when interchangeable follow-on biologics become available, they will face heightened barriers to substitution following the enactment of so-called carve-outs in several states. Data collected to date suggest that a substantial proportion of US physicians remain skeptical of follow-on biologics despite their long record of safe and effective use in Europe. Active surveillance of follow-on biologics within the US market using insurance claims databases can help address this skepticism and help answer key questions concerning the safety of switching between original and follow-on products or between different follow-on products, and of extrapolating to broader indications. Funding is needed to support such surveillance activities and to disseminate the findings to key stakeholders.