CompoundedGuide
Regulatory guide

Compounding Pathways: 503A vs 503B

In the United States, compounded drugs are made through two different legal pathways. Understanding the difference helps you know what rules apply to a compound and what oversight exists.

503A

Traditional Compounding Pharmacy

  • Licensed by the state pharmacy board
  • Requires a valid patient-specific prescription
  • Cannot compound copies of commercially available FDA-approved drugs
  • Regulated under FD&C Act §503A
  • Subject to state pharmacy practice acts and USP <795>/<797> standards
503B

Outsourcing Facility

  • Registered with FDA as an outsourcing facility
  • Can compound without patient-specific prescriptions
  • Must follow current Good Manufacturing Practice (cGMP)
  • Regulated under FD&C Act §503B
  • Subject to FDA inspection and federal oversight

What a full review would check

These are the regulatory factors that determine a compound's compounding pathway:

  1. Federal eligibility — Is the substance on the FDA 503A or 503B bulk drug substances list?
  2. Approved product status — Does an FDA-approved product already exist for this compound? If so, compounding a copy may be restricted.
  3. 503A restrictions — Can a traditional pharmacy compound this, or is it on the "do not compound" list?
  4. 503B restrictions — Can an outsourcing facility compound this, or has FDA identified safety concerns?
  5. Shortage status — Is the drug on the FDA drug shortage list? (Affects compounding of commercial copies.)
  6. Safety signals — Are there FDA warnings, recalls, or adverse event reports associated with this compound?

Why this matters

The pathway a compound takes affects its oversight, quality standards, and legal status. A compound that's eligible under 503A may not be eligible under 503B, and vice versa. Future source adapters would monitor FDA compounding pages, shortage lists, and bulk drug substance lists for changes that affect these determinations.

This is educational information about US compounding law, not legal advice. For specific determinations about a compound's status, consult the FDA compounding page or a qualified attorney.