The distinction generally turns on the molecule's size, complexity, and manufacturing process. Smaller, chemically synthesized polypeptides (such as certain insulin analogues) may be regulated as drugs under CDER, while larger, cell-culture-derived proteins and glycoproteins are typically regulated as biologics under CBER. The regulatory pathway affects which approval or licensure the US manufacturer must hold and which FDA center reviews the foreign facility.

Protein and glycoprotein hormones are typically temperature-sensitive biologics requiring validated cold-chain shipping conditions (often 2–8°C or frozen). Import documentation should include temperature monitoring records for the entire transit, a certificate of analysis with potency and purity data, and evidence of the foreign facility's FDA registration and most recent inspection status. Any temperature excursion during transit must be assessed against validated stability data before the material is released for use.