How compounding pharmacies actually work, 503A, 503B, and why the rules differ by drug

If you have ever been told a medication would be “compounded” for you, or seen a telehealth ad for a compounded version of a drug you recognize, it helps to understand what that word actually means, because it decides how the product is regulated, who is allowed to make it, and whether it has a lawful basis at all. A compounding pharmacy makes a drug to order, combining or altering ingredients for a specific need, rather than dispensing a mass-manufactured product that has cleared FDA’s approval process straight from a drugmaker. That is a legitimate and long-standing part of medicine. It is also the single most misunderstood corner of the current peptide and GLP-1 conversation, because “compounded” is routinely mistaken for “approved,” and the two are not the same thing.

This page is the cross-therapy explainer for how the system works. It covers the two tracks (503A and 503B), the ingredient lists that decide what a pharmacy can use, the drug-shortage exception that briefly opened compounded GLP-1s and has since closed, and the questions worth asking about any compounded product. The therapy-specific versions go deeper for their own audiences: see how compounded peptide prescribing works for the peptide angle and branded versus compounded GLP-1 access in 2026 for the weight-medicine angle.

What is a compounding pharmacy?

A compounding pharmacy prepares a medication tailored to a particular need instead of dispensing a standardized, mass-produced drug. Classic examples are benign and everyday: turning a pill into a liquid for a child or an adult who cannot swallow, leaving out a dye or preservative a patient is allergic to, or combining two ingredients into a single cream. Compounding predates modern drug manufacturing and remains a real clinical tool.

The crucial legal fact sits underneath all of it: a compounded drug does not carry FDA approval. FDA reviews and approves specific manufactured products, a defined formulation, made a defined way, for a defined use, backed by clinical data. A compounded preparation skips that process by design, which is what lets it be individualized, but it also means no agency has verified that particular product’s safety, effectiveness, or quality before it reaches you. That is not a loophole; it is the deliberate trade-off Congress built into the law. It is also why the marketing rules are strict: FDA treats it as a violation of federal law to describe a compounded drug as a “generic version of,” “the same as,” or otherwise equivalent to an approved drug. In September 2025 FDA issued a warning letter to a seller largely over marketing language the agency said wrongly implied its compounded product carried the same standing as the approved one.

503A versus 503B: the two tracks of compounding

Federal law divides compounding into two sections of the Food, Drug, and Cosmetic Act, and almost everything else follows from which one applies. The short version: 503A is the traditional pharmacy compounding one prescription at a time, and 503B is the larger outsourcing facility compounding in batches under manufacturing-grade oversight.

503A: patient-specific, prescription-driven

Section 503A covers the traditional model. A state-licensed pharmacist or physician compounds a drug for an identified individual patient in response to a valid prescription. These pharmacies are primarily overseen by state boards of pharmacy; per FDA, 503A compounders do not register with FDA and are not routinely inspected by the agency in the way manufacturers are. The defining feature is that the product is made for a specific person with a specific prescription, not stocked on a shelf for anyone who wants it.

503B: outsourcing facilities, made in bulk

Section 503B, created by the Drug Quality and Security Act after the 2012 fungal-meningitis outbreak traced to a compounder, created a middle category. An outsourcing facility is a facility that compounds sterile drugs and elects to register with FDA as an outsourcing facility. In exchange, it may compound larger batches and, in many cases, without a patient-specific prescription (for example, to supply a hospital or clinic), but it takes on much heavier obligations: it registers with and is inspected by FDA, and it must comply with current Good Manufacturing Practice (CGMP), the same quality framework that governs drug manufacturers. A 503B facility is closer to a small manufacturer than to a corner pharmacy.

Neither track produces a drug that has cleared FDA approval. The difference is about scale, oversight, and whether an individual prescription is required, not about approval status.

The bulks lists: which ingredients a pharmacy can use

Whether a pharmacy may compound with a given ingredient usually comes down to that ingredient’s status on a specific FDA list, and the tests differ between the two tracks.

Under 503A, a pharmacy may use a bulk drug substance only if it meets one of three tests: the substance complies with an applicable United States Pharmacopeia (USP) or National Formulary (NF) monograph; or, if no monograph exists, it is a component of a drug that already holds full FDA approval; or, failing both, it appears on FDA’s 503A bulks list. That 503A bulks list, codified at 21 CFR 216.23 in a 2019 final rule, is strikingly short, containing only six substances, none of them peptides. Adding anything to it requires full notice-and-comment rulemaking, a process that can run more than a year.

Under 503B, an outsourcing facility may not compound with a bulk drug substance unless that substance appears on the separate 503B bulks list (built around a finding of “clinical need”), or the compounded drug is on FDA’s drug-shortage list at the time it is compounded and dispensed. In both tracks, the bulk substance must also carry a valid certificate of analysis and come from an FDA-registered facility.

There is a third layer that generates most of the confusion in the peptide world: FDA’s interim Category 1 and Category 2 framework for substances still under review. Category 1 means FDA is exercising enforcement discretion, in its own phrase choosing not “to take action” against a compounder that meets the guidance conditions; Category 2 flags substances FDA believes may present “significant safety risks.” These categories come from an interim policy, and FDA has said plainly that being in Category 1 is not the same as being on the bulks list. So a substance can be removed from Category 2 and still have no lawful path to compounding, because removal from a restricted list does not place it on the list that actually authorizes compounding.

The drug-shortage exception, and why it closed for GLP-1s

The shortage exception is the mechanism behind the entire compounded-GLP-1 story, so it is worth understanding on its own. When FDA lists a drug as being in shortage, compounders gain temporary room to make copies of that otherwise-off-limits drug, so patients are not left without a needed medication. The permission is explicitly tied to the shortage: once FDA declares the shortage resolved, the basis for compounding that drug goes away (after short wind-down windows).

That is exactly what happened with the GLP-1 medications. During the tirzepatide and semaglutide shortages, compounded versions proliferated. Then FDA determined the tirzepatide shortage resolved in October 2024 and semaglutide in February 2025, and the enforcement-discretion wind-down periods for compounding them ran out in spring 2025. With the shortages over and these drugs not on the 503B bulks list, there is no general shortage-based basis to compound them anymore. FDA has since moved to shut the door more firmly: on April 30, 2026 it proposed to permanently exclude semaglutide, tirzepatide, and liraglutide from the 503B bulks list. That remains a proposal, not a final rule, as of this writing, but the direction is clear, and FDA has backed it with enforcement, including a round of warning letters to 30 telehealth companies in March 2026 over compounded-GLP-1 marketing. Some states have gone further on their own: Kentucky’s pharmacy board, for instance, has barred compounding semaglutide and tirzepatide as “essentially copies” now that they are off the shortage list.

A narrow patient-specific 503A route can remain where a prescriber documents a genuine clinical need the approved product cannot meet, such as a real allergy to an inactive ingredient or a dose the manufactured product does not offer. That is a case-by-case clinical judgment, not a flat monthly subscription to a compounded copy, and it is a question for your prescriber, not a marketing claim. The branded products themselves are FDA-approved and can be described that way: semaglutide as Ozempic and Wegovy, tirzepatide as Mounjaro and Zepbound. Our weight-medicine partner site covers the practical access side in branded versus compounded GLP-1 access in 2026.

Where do peptides fit in?

Approved drugs start with an advantage under these rules: an FDA-approved drug’s active ingredient is, by definition, a component of an approved drug, and often has a monograph too, so there is a recognized starting point for compounding it. Most of the peptides discussed online, such as BPC-157, TB-500 or CJC-1295, are not FDA-approved drugs, so their position depends on the list and category rules above, and it has been the subject of FDA review in 2024 and 2026. Rather than repeat that here, we keep one plain-English line per substance, dated and refreshed monthly, in our peptide status explainer. For the peptide-specific prescribing mechanics, see how compounded peptide prescribing works.

What to ask about any compounded medication

You do not need to memorize the statute to protect yourself; you need a few questions that map onto the framework above. First, is the underlying drug FDA-approved, or is it a substance with no monograph, no approved-drug component, and no spot on a bulks list? Second, if a shortage exception is being invoked, is the drug actually on FDA’s current shortage list today, or did that shortage end (as the GLP-1 shortages did)? Third, is the pharmacy a state-licensed 503A pharmacy filling a patient-specific prescription, or a registered 503B outsourcing facility, and does the arrangement match, a true individualized prescription versus a one-size-fits-all monthly plan?

A few warning signs cut across all of it. Marketing that calls a compounded product a “generic” of a brand-name drug, or “the same as” an approved one, is describing something FDA has repeatedly said is not allowed, and is a signal the seller is not being careful with the law. So is any promise that a prescription is a foregone conclusion, or a questionnaire-only intake for a complex or controlled therapy where a real clinical evaluation should happen. None of this is medical or legal advice; it is a way to ask better questions before you hand over a payment. If a source cannot answer the ingredient-status question clearly, that itself is an answer.

The bottom line

Compounding is a legitimate part of medicine with two lawful tracks: 503A pharmacies compounding for individual patients under a prescription, and 503B outsourcing facilities compounding in bulk under FDA registration and manufacturing rules. Neither one produces a drug that has cleared FDA approval, and what any pharmacy may lawfully compound turns on the ingredient’s list status, a monograph, an approved-drug component, or a place on the relevant bulks list, plus a shortage exception that lasts only as long as the shortage. That is why approved drugs generally have a compounding starting point, and why the GLP-1 shortage window opened and then closed. When you understand the tracks and the lists, the marketing gets a lot easier to read, and the questions worth asking get a lot sharper.

Educational information only, not medical advice. Every regulatory statement on this page is dated and sourced to the primary FDA and Federal Register documents linked above. As of October 12, 2026, no final rule on the proposed 503B GLP-1 exclusion had been published; this page will be updated as the record changes.