What is polymorphism in crystallization and why is it critical in pharmaceutical manufacturing?

Polymorphism is the ability of a compound to exist in multiple crystal structures with identical chemical composition but different lattice arrangements. Different polymorphs have different solubility, dissolution rate, bioavailability, and stability. In pharmaceuticals, the wrong polymorph can be therapeutically inactive or unstable. Control methods: seeding with desired polymorph, precise temperature/supersaturation control, solvent selection (influences nucleation kinetics), ultrasound to control nucleation, and PAT monitoring (Raman, FBRM) for real-time form verification.