503A and 503B

Sections 503A and 503B of the Federal Food, Drug, and Cosmetic Act establish two distinct regulatory pathways for pharmacy compounding, created by the Drug Quality and Security Act of 2013. A 503A compounder is a state-licensed pharmacy that compounds under a patient-specific prescription, regulated primarily by the state board of pharmacy with limited FDA oversight. A 503B outsourcing facility is FDA-registered, may compound for office use without patient-specific prescriptions, and operates under cGMP requirements.

How 503A and 503B work

The 503A pathway is the traditional pharmacy compounding model. A 503A pharmacy compounds in response to a specific prescription written for an identified patient, uses bulk drug substances that comply with USP standards or appear on FDA's 503A bulk drug substances list, and operates under USP 797 (sterile compounding) and USP 800 (hazardous drugs) practice standards enforced through state board inspection. Federal jurisdiction attaches when a 503A pharmacy compounds for office use without a patient-specific prescription, ships interstate at scale, or violates the bulk drug substances framework.

The 503B pathway is the outsourcing facility model. A 503B registers with FDA, pays an annual user fee, submits to FDA inspection, complies with cGMP requirements (21 CFR Parts 210 and 211 with FDA's draft cGMP guidance for 503B), reports adverse events, and may compound for office use. 503B compounders may use only bulk drug substances on FDA's 503B bulks list (a narrower list than 503A's), unless the drug is on FDA's shortage list. The April 30, 2026 FDA proposal to exclude semaglutide from the 503B bulks list illustrates the regulatory leverage FDA exercises through bulks-list decisions.

When 503A and 503B apply

A pharmacy's operational profile selects its regulatory pathway. A pharmacy compounding under patient-specific prescriptions for retail dispensing operates as 503A. A pharmacy compounding office-use stock for physician practices, hospitals, or surgical centers must register as 503B. The same physical facility cannot operate as both pathways simultaneously; the regulatory framework treats them as distinct legal entities even where the corporate structure shares ownership.

The compounder's exposure under each pathway

A 503A compounder's regulatory exposure runs through the state board (license suspension, revocation, fines), FDA's enforcement authority where the compounder operates outside the 503A framework, and DEA where controlled substances are involved. A 503B compounder's regulatory exposure runs through FDA's full enforcement authority (Form 483, Warning Letter, consent decree, injunction, criminal referral), cGMP compliance audits, and the 503B bulks list framework. The most acute current exposure (2026) sits in GLP-1 and peptide compounding, where the FDA Bulks List rulemaking and the dispense-date defense framework determine whether ongoing operations are defensible.

Related terms

• USP 797 / 800 The sterile compounding and hazardous drug standards that govern compounding operations under both pathways.
• False Claims Act The civil enforcement framework when compounding billing is alleged to violate federal program rules.
• Anti-kickback statute The criminal statute that surfaces in compounding referral-pattern investigations.

See also

• Practice area
  Compounding Pharmacy Defense

  The full compounding defense framework spanning 503A and 503B regulatory pathways, FDA enforcement, and state board inquiries.

• Practice area
  503A Defense

  503A-specific defense framework: patient-specific prescription compliance, state board oversight, USP 797 compliance.

• Practice area
  503B Defense

  503B outsourcing facility defense: cGMP compliance, FDA inspection response, bulks list disputes.