Health professionals are compounding when they prepare a specialized drug product to fill an individual patient's prescription when an approved drug can't fill the bill.

Compounding sometimes involves nothing more than crushing a pill into a powder with a mortar and pestle and then mixing it into a liquid, says Wayne Mitchell, an FDA regulatory counsel and member of the agency's internal pharmacy compounding steering committee. On the other hand, some types of compounding involve sophisticated scientific operations. Preparing sterile drug products, for example, can require complex steps to ensure a germ-free work environment.

Here are some of the types of delivery systems we compound: