The 503A Bulks List, Explained: Category 1 vs Category 2

Every article about peptide regulation uses the same six phrases — 503A, 503B, the bulks list, category 1, category 2, nomination — and almost none of them defines any of them. That is not an accident. The vocabulary is doing work in those articles: "BPC-157 is a category 2 substance" sounds like a classification within a system of permissions, and readers reasonably assume that being in the system means being allowed somewhere in it.

It does not. Here is the whole vocabulary, in the order it actually matters, checked against the regulation and FDA's own pages on August 11, 2026.

Start with the only sentence that grants permission

Section 503A of the Federal Food, Drug, and Cosmetic Act is the provision that lets a state-licensed pharmacist or physician compound a drug for an individual patient without the drug being FDA-approved. It is an exemption, and like every exemption it has conditions.

One of those conditions governs the raw ingredient — the bulk drug substance. FDA states it on its own page in three bullets. A compounder may only use a bulk drug substance that¹:

1. 1.complies with an applicable USP or NF monograph, if one exists, and the USP chapter on pharmacy compounding; or
2. 2.is a component of an FDA-approved drug product, if no applicable monograph exists; or
3. 3.appears on FDA's list of bulk drug substances that can be used in compounding — the 503A bulks list — if there is no monograph and it is not a component of an approved drug.

That is the entire universe of lawful bulk substances. Three doors. A substance that goes through none of them cannot lawfully be used, and no category, classification, posture, recommendation or vote adds a fourth door.

Two further conditions apply regardless: the substance must be accompanied by a valid certificate of analysis, and it must have been manufactured by an establishment registered with FDA¹. That second one quietly disqualifies most of what is sold online as "research grade".

The list itself is six substances long

The 503A bulks list is codified at 21 CFR 216.23. People discuss it as though it were a large registry. It is not. In full, as of the eCFR's current issue²:

• •Brilliant Blue G
• •Cantharidin (for topical use only)
• •Diphenylcyclopropenone (for topical use only)
• •N-acetyl-D-glucosamine (for topical use only)
• •Squaric acid dibutyl ester (for topical use only)
• •Thymol iodide (for topical use only)

Six substances. Five of the six are restricted to topical use. No peptide has ever appeared on it.

The same regulation also names four substances FDA considered and declined to list: oxitriptan, piracetam, silver protein mild, and tranilast². That paragraph is worth knowing exists, because it establishes that "FDA evaluated it" and "FDA listed it" are genuinely different outcomes, and the regulation records both.

503A versus 503B: the difference is who is compounding

These get used interchangeably and they are not interchangeable.

Section 503A covers the traditional pharmacy or physician compounding for an identified individual patient, usually against a prescription. This is the section that governs the pharmacy your telehealth clinic sends your prescription to.

Section 503B covers outsourcing facilities — larger operations that register with FDA, are inspected on a risk-based schedule, and may compound in bulk without patient-specific prescriptions. They have their own separate bulks list, developed under a different standard: substances for which there is a clinical need.

Why it matters to a reader: the two lists are not the same list, and a substance's standing under one says nothing about its standing under the other. Ipamorelin is the clean example. It sits in category 2 under the 503B interim policy while its 503A nomination sits in the withdrawn table — one substance, two postures, in two different systems³. Anyone who tells you "ipamorelin is category 2" has told you about half of it.

Categories 1, 2 and 3 are not tiers of permission

This is the part every other page gets wrong, so read it slowly.

While FDA works through the nominations, it published an interim policy describing how it intends to exercise enforcement discretion. The categories exist only inside that policy. FDA's own descriptions¹:

• •Category 1 — nominated with sufficient information to evaluate, does not appear on any other list, and may be eligible for the bulks list. FDA does not intend to take action against a compounder using it, provided the conditions in the guidance are met.
• •Category 2 — nominated with sufficient information, but FDA has identified significant safety risks. FDA would consider taking action against a compounder using it under its general enforcement policies.
• •Category 3 — nominated with insufficient information for FDA to evaluate. Also not eligible for the category 1 policy; FDA would consider taking action.

Now the sentence that changes how you read all three: category 1 is a statement about what FDA intends to do, not about what the law permits. It is prosecutorial discretion, published in a guidance document, and FDA says plainly that a substance stays within the interim policy "until the agency decides on inclusion" or "unless the agency removes the substances from category 1 based on, for example, information about safety risks"¹.

A compounder relying on category 1 is not operating lawfully under 503A. It is operating unlawfully in a way FDA has said it does not currently plan to pursue. Those are different things, and the difference is the entire distance between a durable business and one that ends with a letter.

Category 2 is worse than not being categorized at all, because it is an affirmative published finding of safety risk. And leaving category 2 does not promote a substance to category 1 — a point worth holding onto, because in April 2026 twelve peptides left category 2 at once and it was widely reported as a loosening. It was not. They were moved into a table of nominations that were withdrawn by the nominators³, which is a procedural event, not a safety clearance. Which peptides, and what it means for each, is the subject of our peptide regulatory status tracker.

One more piece of housekeeping most write-ups have not caught up with: FDA issued guidance stating that it does not intend to place bulk drug substances nominated on or after January 7, 2025 into these categories at all¹⁴. The category system is closing to new entrants.

How a substance actually gets on the list

Five stages. Only the last one changes anything.

1. 1.Nomination. Anyone may nominate a bulk substance.
2. 2.FDA's four-factor review. The factors are written into the regulation itself, and they are narrower than people assume — this is not a benefit-risk assessment of the drug. Verbatim from 21 CFR 216.23(c), FDA evaluates: "the physical and chemical characterization of the substance"; "any safety issues raised by the use of the substance in compounded drug products"; "the available evidence of the effectiveness or lack of effectiveness of a drug product compounded with the substance, if any such evidence exists"; and "historical use of the substance in compounded drug products, including information about the medical condition(s) the substance has been used to treat and any references in peer-reviewed medical literature"².
3. 3.The Pharmacy Compounding Advisory Committee advises. This is the step that happened on July 23–24, 2026. FDA states on its own meeting page that advisory committees "make non-binding recommendations to the FDA, which generally follows the recommendations but is not legally bound to do so"⁵.
4. 4.Proposed rule, with a public comment period.
5. 5.Final rule. This is the only step that puts a substance on the list.

Note what stage 2 does not include. There is no factor for "does this work for the use it is marketed for". The closest is factor three, and it is satisfied by evidence of effectiveness or lack of effectiveness, if any such evidence exists — a phrase that anticipates there being none.

How long stages 4 and 5 take: the number nobody quotes

You will see "a proposed rule within 9 to 18 months" repeated widely. It appears on vendor and affiliate blogs and in no FDA document. FDA has published no timeline.

Here is what the record actually supports, and it is on FDA's own page.

The first 503A bulks rulemaking ran from advisory meetings in 2015–16 to a final rule published February 19, 2019 and effective March 21, 2019 — roughly three years⁶.

The second is more instructive, because it has not finished. On September 5, 2019, FDA issued a proposed rule proposing to place five substances on the list and to decline twenty-six others (84 FR 46688, Docket FDA-2018-N-4845)⁷. FDA's own page still describes it in the future tense: "After considering public comments, the agency will issue a final regulation"¹.

That proposed rule is approaching its seventh year without a final rule. If you want a realistic answer to "when will BPC-157 be legal to compound", that is the honest comparison — not a figure invented by people selling it.

What a listing would and would not mean

Suppose the rulemaking succeeds and a peptide lands on 21 CFR 216.23. Three things would still be true.

It would not be an approved drug. The bulks list governs an ingredient a pharmacy may use. It is not a marketing authorization, there is no approved label, and no efficacy finding has been made.

Calling it FDA-approved would be a legal problem, not just an inaccuracy. 21 CFR 216.23(d) states, verbatim, that any person who represents that a compounded drug made with a bulk substance that appears on this list is "FDA approved, or otherwise endorsed by FDA generally or for a particular indication, will cause the drug to be misbranded" under sections 502(a) and/or 502(bb) of the Act². Read the placement of that clause: it binds sellers of substances that have already completed rulemaking. The regulation anticipated this exact marketing wave and pre-emptively made it a misbranding issue.

The same paragraph opens by stating that "there are inadequate data to demonstrate the safety or efficacy of any drug product compounded using any of the drug substances listed"² — said of the six substances that are on the list.

Nothing would change for a tested athlete. WADA classification and US compounding policy are separate instruments in separate jurisdictions, and a compounding-list entry is not the marketing authorization that WADA's S0 class turns on. See the WADA prohibited list for peptides, or check a specific compound in the prohibited-status checker.

Putting it together

If someone tells you a peptide is "approved for compounding", the check takes about a minute:

• •Is it on 21 CFR 216.23(a)? If not, door three is closed.
• •Is it a component of an FDA-approved drug product? If not, door two is closed.
• •Is there an applicable USP or NF monograph? If not, door one is closed.

Three noes means no lawful basis, whatever category anything is in and whatever any committee recommended. For the current answer on each compound, with the date each check was performed and every source linked, use the peptide regulatory status tracker. For what happened in the room in July 2026 — who voted, who appointed them, and what FDA's own scientists recommended — read the FDA peptide advisory vote. And for the broader legal picture including research-chemical sales, see are peptides legal?.