The 503A Bulk Drug Substances List: What Can Legitimately Be Compounded

The 503A compounding regulatory framework is the legal infrastructure that makes legitimate compounded medications possible in the United States. The framework permits state-licensed pharmacies to prepare medications for individual patients based on valid prescriptions — but only using specific ingredients on a specific FDA-recognized list.

The list — the "bulk drug substances eligible for use in compounding under section 503A" — is one of the most consequential and least-discussed documents in the compounded-medication space. Understanding what is on it (and what is not) explains why some peptides can be legitimately compounded and most "research peptides" cannot.

This post is a plain-English walkthrough.

The legal foundation

The 503A compounding pathway is defined by Section 503A of the Federal Food, Drug, and Cosmetic Act, originally enacted as part of the Food and Drug Administration Modernization Act of 1997 and revised by the Drug Quality and Security Act (DQSA) of 2013.

The statute permits state-licensed pharmacies to prepare compounded medications without FDA approval of each finished product, provided the compounding meets specific criteria:

• The compounded preparation is for an individual identifiable patient
• A valid prescription from a licensed prescriber exists
• The compounding pharmacy is appropriately licensed by the state
• The bulk drug substance used meets one of three eligibility categories

The third criterion — bulk drug substance eligibility — is the part most patients (and many prescribers) misunderstand. Compounding is not a license to make anything. It is a license to make specific things, in specific ways, for specific patients.

The three eligibility categories

A bulk drug substance can be used in 503A compounding only if it falls into one of these three categories:

Category 1: Component of an FDA-approved drug

If a bulk drug substance is the active pharmaceutical ingredient of an FDA-approved drug product, it is eligible. This is the largest category and accounts for most legitimate compounding.

Examples relevant to telehealth peptide therapy:

• Semaglutide — active ingredient of FDA-approved branded products
• Tirzepatide — active ingredient of FDA-approved branded products
• Liraglutide — active ingredient of FDA-approved branded products
• Testosterone — active ingredient of multiple approved formulations
• Estradiol — active ingredient of approved hormone-replacement products

When you read about "compounded semaglutide" or "compounded tirzepatide," this is the category they fall under. The active ingredient is the same molecule as in the approved branded product; the compounding pharmacy prepares a finished product using that ingredient under a specific patient's prescription.

Category 2: USP or National Formulary monograph

The United States Pharmacopeia (USP) and National Formulary (NF) publish official monographs for pharmaceutical ingredients — quality standards including identity, purity, potency, and analytical methods.

Ingredients with a published USP or NF monograph are eligible for 503A compounding. The monograph itself is the quality standard the compounder must meet.

Examples relevant to peptide therapy:

• Sermorelin — has a USP monograph
• NAD+ (nicotinamide adenine dinucleotide) — has a monograph
• B12 (cyanocobalamin) — has a monograph
• L-carnitine — has a monograph
• Glutathione — has a monograph

This is why sermorelin can be legitimately compounded even though branded sermorelin products have specific approved formulations: the underlying active ingredient has a USP monograph that establishes the quality standard.

Category 3: FDA bulk drug substances list

For ingredients that do not fit categories 1 or 2, FDA can explicitly add them to the bulk drug substances list through a formal nomination and review process. The Pharmacy Compounding Advisory Committee evaluates each nomination based on:

• Physical and chemical characterization
• Safety profile
• Effectiveness for the proposed use
• Historical use in compounding
• Whether an FDA-approved drug product is available for the same use

The list is published as 21 CFR Part 216 and is updated periodically. As of 2026, the list includes a relatively small number of substances — a few dozen — most of which are for niche compounding indications.

Adding a substance to this list takes years. The nomination process involves data submission, public comment, advisory committee review, and final rulemaking. This is not a fast-track pathway.

What is NOT eligible

Everything outside the three categories is not eligible for legitimate 503A compounding. This includes:

Investigational drugs in clinical trials

Retatrutide, MariTide (maridebart cafraglutide), mazdutide, pemvidutide, petrelintide, orforglipron, and other compounds on the 12-peptide watchlist are not eligible. They are not components of FDA-approved drugs (because they are not approved), have no USP monograph, and are not on the bulk drug substances list.

Pharmacies offering "compounded retatrutide" or any compounded version of an investigational compound are operating outside the legal framework. We cover this in detail in compounded investigational peptides are not legitimate.

Research-grade peptides without approved-drug status

BPC-157, TB-500 (thymosin beta-4), epitalon, MOTS-c, humanin, AOD-9604, MK-677, and similar compounds widely sold as "research peptides" are not eligible. None has FDA approval, none has a USP monograph, and none has been added to the bulk drug substances list.

In some cases (BPC-157 is the most prominent), FDA has explicitly evaluated the compound and placed it in a "Category 2" of substances unsuitable for compounding due to safety and efficacy concerns. This is the strongest possible signal that the compound is outside the legitimate compounding framework.

Foreign-approved drugs not approved in the US

Pharmaceuticals approved in other regulatory jurisdictions but not in the US (mazdutide in China is the most relevant 2026 example for telehealth peptide therapy) are not eligible for US compounding. International regulatory status does not transfer.

"Pharmaceutical-grade" peptides sold as bulk powder

Vendors who sell bulk peptide powder labeled "pharmaceutical grade" or "research grade" do not transform their products into compoundable ingredients by labeling. The substance has to meet the three-category eligibility test regardless of marketing claims.

The FDA shortage list interaction

A specific overlap matters: when an FDA-approved drug is on the FDA Drug Shortages list, 503A pharmacies are explicitly permitted to compound essentially copies of the approved drug to address the shortage. This is the pathway that enabled the rise of legally compounded semaglutide and tirzepatide during the 2022-2024 shortage windows.

The shortage pathway requires:

• The drug must be FDA-approved (Category 1 eligibility above)
• The drug must be on FDA's official shortage list

When semaglutide was removed from the FDA shortage list in early 2025, the compounding rules for it changed accordingly — the shortage-specific pathway closed, though the Category 1 eligibility (component of an FDA-approved drug) continues to support compounding under more constrained circumstances. The current regulatory situation for compounded GLP-1 is detailed in our 503A vs 503B compounding pharmacies post.

Why the framework matters

The bulk drug substances framework is the practical line between legitimate compounded medication and outside-the-regulatory-system "research peptide" supply.

When you receive compounded semaglutide from a licensed 503A pharmacy through a US-licensed clinician's prescription, the entire supply chain is operating within the framework:

• The pharmacy is licensed by its state board
• The clinician is licensed by their state medical board
• The active ingredient is eligible (Category 1: component of approved drug)
• The preparation follows USP 795/797 quality standards
• The patient relationship and prescription are valid

When you order BPC-157 or research-grade MOTS-c from an online vendor, none of these elements apply. The ingredient is not eligible. The vendor is not a licensed pharmacy. There is no prescription. There is no clinician. The "research only, not for human consumption" disclaimer is the vendor's legal protection — and it accurately describes what you are buying.

The difference is not a matter of opinion or marketing positioning. It is a matter of which federal statute applies.

How to verify legitimacy

For any compounded peptide or medication, you can verify legitimacy by checking:

1. Is the active ingredient on one of the three eligibility paths? Approved drug component, USP monograph, or bulk drug substances list. Search the FDA databases or ask the pharmacy directly.

2. Is the dispensing pharmacy licensed as 503A or 503B? State pharmacy board lookup tools confirm licensure status.

3. Is the prescriber a US-licensed clinician in your state? State medical board lookup tools verify license status.

4. Does the medication arrive with a valid prescription label? Patient name, clinician name, pharmacy name, lot number, beyond-use date. Generic or unlabeled vials are a red flag.

If any of the four checks fails, the medication is operating outside the framework regardless of marketing claims.

What patients can actually access

In 2026, through legitimate 503A/503B compounding pathways with US-licensed clinicians, the following peptides and peptide-adjacent compounds are accessible:

• Semaglutide (compounded)
• Tirzepatide (compounded)
• Liraglutide (compounded, less common)
• Sermorelin (USP monograph)
• Tesamorelin (FDA-approved branded; compounded versions also available)
• NAD+ (USP monograph)
• B12 / methylcobalamin (USP monograph)
• L-carnitine (USP monograph)
• Glutathione (USP monograph)
• Sermorelin/CJC-1295/ipamorelin (more complex regulatory status — varies by pharmacy and state)

Outside this list, with very few exceptions, compounded availability is not legitimate.

The TelePeptide prescribing model operates within this framework. Programs cover the legitimate scope; investigational compounds and research-grade peptides are explicitly outside scope until and unless they reach approval or USP monograph status.

Bottom line

The 503A bulk drug substances eligibility framework defines what can be legitimately compounded in the United States. Three categories: components of FDA-approved drugs, USP/NF monograph ingredients, and the FDA bulk drug substances list. Compounded semaglutide and tirzepatide are eligible because they fall in category 1. Sermorelin, NAD+, B12, glutathione, and similar peptides are eligible because they fall in category 2. BPC-157, TB-500, retatrutide, MariTide, and the broader "research peptide" market are not eligible because they fall outside all three categories. The framework is the practical difference between a legitimate prescription and a vial of unverified research chemical. Verify before purchasing.