FDA 503A Category System — VialBase News
FDA 503A Category System
The FDA 503A Category System is the framework the FDA uses to evaluate and classify bulk drug substances that may be used in compounding by pharmacies operating under Section 503A of the Federal Food, Drug, and Cosmetic Act (FD&C Act).
Background: Section 503A
Section 503A of the FD&C Act provides exemptions from certain FDA requirements for pharmacies that compound drugs for individual patients based on valid prescriptions. To qualify for these exemptions, pharmacies must meet specific conditions, including only using bulk drug substances that appear on an FDA-approved list or that meet certain criteria.
The FDA maintains a list of bulk drug substances that have been evaluated for use in compounding. Each substance is placed into one of three categories based on the FDA’s assessment.
The Three Categories
Category 1 — Can Be Compounded
Substances in Category 1 have been evaluated by the FDA and determined to be acceptable for use in compounding under Section 503A. This means:
- Licensed compounding pharmacies can prepare medications using these substances
- A valid patient-specific prescription is required
- The pharmacy must meet all other 503A requirements (state licensing, etc.)
- The compounded product cannot be a copy of an FDA-approved drug that is commercially available
Examples of Category 1 substances (as of April 2026):
- Various hormone compounds (testosterone, progesterone, estradiol)
- Certain vitamins and supplements in injectable form
- Selected peptides under review for reclassification
Category 2 — Cannot Be Compounded (Restricted)
Substances in Category 2 have been evaluated and the FDA has determined they present significant safety or other concerns that make them inappropriate for compounding under 503A. This means:
- Compounding pharmacies cannot legally prepare medications using these substances
- This applies to both 503A pharmacies (patient-specific prescriptions) and limits availability through 503B outsourcing facilities
- The substances are not illegal to possess but cannot be compounded by pharmacies
Peptides currently on Category 2 (as of April 2026, pending reclassification):
- BPC-157
- TB-500 (Thymosin Beta-4)
- CJC-1295
- Ipamorelin
- GHRP-2
- GHRP-6
- AOD-9604
- Melanotan II
See FDA-Category-2-Designations-2023-2024 for the history of these designations.
Category 3 — Under Evaluation
Substances in Category 3 are currently being reviewed by the FDA. They have been nominated for inclusion on the compounding list but the FDA has not yet completed its evaluation. During evaluation:
- The substance’s status for compounding is uncertain
- Some pharmacies may continue compounding at their own risk
- FDA may request additional data from nominators
The Evaluation Process
The FDA evaluates nominated bulk drug substances using several criteria:
- Safety: Is the substance safe for use in compounding? Are there known adverse effects?
- Physicochemical characterization: Is the substance well-characterized? Can it be reliably identified and tested?
- History of use: Has the substance been used historically in compounding? What is the clinical evidence base?
- Evidence of efficacy: Is there adequate evidence that the substance is effective for its intended use?
- Availability of alternatives: Are there FDA-approved alternatives available?
The Pharmacy Compounding Advisory Committee (PCAC) reviews nominated substances and makes recommendations to the FDA.
503A vs 503B
It is important to distinguish between the two compounding exemptions:
| Feature | 503A | 503B |
|---|---|---|
| Type | Traditional pharmacy | Outsourcing facility |
| Prescription | Required (patient-specific) | Not required (can compound in advance) |
| Registration | State-licensed | FDA-registered |
| Inspection | State boards | FDA (similar to manufacturers) |
| Scale | Individual prescriptions | Larger batches |
| Drug list | 503A bulk drug substance list | Different evaluation framework |
The Category 2 designations primarily affect 503A pharmacies, but they also signal FDA concerns that affect 503B facilities.
Pending Kennedy Reclassification
In February 2026, HHS Secretary Robert F. Kennedy Jr. announced intent to reclassify 14+ peptides from Category 2 back to Category 1. See FDA-Reclassification-Announcement-Feb-2026 for details.
As of April 2026:
- The formal reclassification process has not been completed
- Category 2 designations remain in effect
- The FDA continues to enforce current classifications — see FDA-Warning-Letters-April-2026
- Compounding pharmacies should not resume peptide compounding until formal reclassification is published
Related Notes
- FDA-Category-2-Designations-2023-2024 — initial wave of peptide restrictions
- FDA-Reclassification-Announcement-Feb-2026 — Kennedy’s proposed reversal
- FDA-Warning-Letters-April-2026 — continued enforcement under current rules
- Semaglutide-Compounding-Shortage-Resolution — related compounding regulatory issue