On March 9, The New York Academy of Sciences will present “Scientific Considerations for Complex Drugs in Light of Established Regulatory Guidance,” a full-day conference exploring current definitions, regulatory hurdles, and future challenges for follow-on versions of complex drugs. However, current U.S. regulations do not make scientific distinctions between small-molecule drugs and non-biological complex drugs; although the latter may present many of the same scientific and clinical challenges to reproduce as biologics.