503A vs 503B Compounding Pharmacies: Who Oversees Your Compounded GLP-1

A 503A pharmacy is a state-licensed pharmacy that compounds a drug for one named patient against a prescription. Its state board of pharmacy oversees it day to day, it does not have to follow federal manufacturing rules (CGMP), and federal law does not make it report side effects to FDA.^[1][4][10] A 503B outsourcing facility chooses to register with FDA. In return it must meet CGMP, is inspected by FDA on a risk-based schedule, must report adverse events, and may supply clinics without a patient name on the order.^[1][2] FDA’s register listed 98 outsourcing facilities as of October 2026.^[3] Of the 68 pharmacies we track behind telehealth GLP-1 sellers, 61 do not appear on that register. A pharmacy that is not on it is usually a state-licensed 503A pharmacy, which its state license confirms.

503A vs 503B: the differences side by side

Each row comes from the statute or from FDA’s description of it.^{[1][2][4][6][7][8][9]} The rest of this article explains the rows that matter most if you are buying compounded semaglutide or tirzepatide.

What a 503A pharmacy is

Section 503A is the older route. It is what most people picture when they hear “compounding pharmacy”: a pharmacist preparing a medicine for one patient. The law gives the drug an exemption from FDA approval, CGMP and some labeling rules, but only if it is compounded for a particular person.^[1]

…compounded for an identified individual patient based on the receipt of a valid prescription order or a notation, approved by the prescribing practitioner, on the prescription order that a compounded product is necessary for the identified patient…

— 21 U.S.C. 353a(a), section 503A of the FD&C Act

A 503A pharmacy may make a batch ahead of time, but only “in limited quantities” and only based on a history of prescriptions it has actually received.^[8] It cannot fill a clinic’s order for office stock with no patient named; that is the 503B route.^[1] The statute also caps out-of-state shipping at 5% of the pharmacy’s prescriptions unless its state has signed a memorandum of understanding with FDA.^[8]

Oversight happens mostly at the state level. In FDA’s words, “state boards of pharmacy have primary responsibility for the day-to-day oversight” of these pharmacies, while FDA “does conduct surveillance and for-cause inspections” of them.^[4] A 503A pharmacy is not held to CGMP, the standard drug makers follow.^[4] Federal law also does not require it to report adverse events to FDA. FDA says this means side effects from compounded GLP-1s are probably underreported.^[10]

Where a 503A pharmacy gets its ingredient

A 503A pharmacy may only compound from a bulk ingredient that meets one of three tests. The ingredient follows a USP or NF monograph. Or it is a component of an FDA-approved drug. Or it is on FDA’s 503A bulks list.^[6] Semaglutide and tirzepatide are components of approved drugs, so a 503A pharmacy can use them as ingredients. What limits it is a different rule.

The “essentially a copy” limit

Section 503A bars a pharmacy from compounding, “regularly or in inordinate amounts,” drugs that are “essentially copies of a commercially available drug product.”^[8] A change made for one patient that the prescriber decides makes “a significant difference” for that patient does not count as a copy.^[8] FDA has said it will not act against a pharmacy that fills four or fewer prescriptions of a copy in a calendar month.^[5] FDA has also said that adding vitamin B12 to semaglutide may still count as a copy.^[5] A telehealth program shipping the same formula to thousands of members is far past four a month. That is why the “personalized dose” language on seller sites matters to their legal position.

What a 503B outsourcing facility is

Section 503B was added by the Drug Quality and Security Act, enacted on November 27, 2013.^[1] Congress passed it after the 2012 meningitis outbreak, which FDA links to contaminated drugs from a Massachusetts compounding pharmacy: more than 750 infections and more than 60 deaths.^[1] The law created a new, voluntary category of compounder.

The law defines an outsourcing facility as a facility at one geographic location or address that is engaged in the compounding of sterile drugs; has elected to register as an outsourcing facility; and complies with all of the requirements of section 503B.

— FDA, Information for Outsourcing Facilities

The trade-off is scale for scrutiny. An outsourcing facility can compound without a patient-specific prescription. It can fill a hospital or clinic order for office stock.^[1] In return:

• CGMP applies. 503B drugs are exempt from FDA approval but not from current good manufacturing practice.^[2]
• FDA inspects. The statute directs FDA to inspect outsourcing facilities on a risk-based schedule. That schedule weighs compliance history, recalls and other factors.^[9]
• Adverse events must be reported. “Outsourcing facilities shall submit adverse event reports” to FDA.^[9]
• FDA gets a product list. Each facility tells FDA what it compounded in the last six months when it registers, then every June and December.^[2][9]
• The label names the maker. A 503B label must carry “This is a compounded drug.” and the facility’s name, address and phone number. It must also show a lot number, the compounding date, an expiration date and “Not for resale.” If the drug was not dispensed on a prescription for a named patient, it must also say “Office Use Only.”^[9]
• No middlemen. Only the facility that made the drug may sell or transfer it. Giving it in a health care setting or dispensing it on a prescription is still allowed.^[9]

An outsourcing facility is also barred from compounding anything the statute calls “essentially a copy of one or more approved drugs.”^[9] It may only start from a bulk ingredient on the 503B bulks list, or for a drug on FDA’s shortage list “at the time of compounding, distribution and dispensing.”^[7] Being a component of an approved drug does not help here, unlike under 503A. That is a narrower door for GLP-1s.

Which is safer, 503A or 503B?

Neither is FDA-approved. FDA does not review either kind of compounded drug for safety, effectiveness or quality before it reaches patients.^[1] The difference is who checks the building and how often. A 503B facility answers to FDA and to manufacturing-grade standards. A 503A pharmacy answers mainly to its state board.^[4]

Registration is also not the same as inspection. Of the 98 facilities on FDA’s register in the October 2026 copy, 42 were marked “Not yet inspected” and 56 had an inspection date.^[3] Most of the uninspected ones registered recently. The breakdown is in our analysis of FDA’s outsourcing facility register. A 503B name on a box tells you which rules apply. It does not tell you the last inspection went well.

Two things hold for both. FDA can act against either on quality grounds, whatever the shortage status.^[5] And because 503A pharmacies do not have to report side effects to FDA, nobody has a full count of harms from compounded GLP-1s. What FDA’s adverse event reports can and cannot show covers that gap.

What changed for compounded GLP-1s when the shortages ended

While semaglutide and tirzepatide were on FDA’s shortage list, both routes had room. The 503A copy limit applies to drugs that are “commercially available,” and FDA generally treats a drug as commercially available once its shortage is resolved. 503B facilities could compound from bulk only because the drugs were on the shortage list.^[5][7] When the shortages ended, FDA gave each route a separate grace period. 503B facilities got 30 more days than 503A pharmacies.^[5]

FDA’s own timeline is the source for every date in the table.^[5] The grace periods only covered violations tied to the shortage. FDA said it could still act on anything else, including “findings that a product may be of substandard quality or otherwise unsafe.”^[5]

The routes now look different. Semaglutide or tirzepatide can still come from a 503A pharmacy when the patient’s prescriber documents a significant clinical difference. It can also stay within the four-a-month limit on copies.^[5][8] A 503B facility has a harder problem. Neither drug is on the shortage list or the 503B bulks list.^[5] On April 30, 2026, FDA proposed keeping semaglutide, tirzepatide and liraglutide off that list for good. In FDA’s assessment, outsourcing facilities have no clinical need to make them from bulk ingredients.^[11]

When FDA-approved drugs are available, outsourcing facilities cannot lawfully compound using bulk drug substances unless there is a clear clinical need.

— FDA Commissioner Marty Makary, April 30, 2026

FDA later extended the comment period to July 30, 2026.^[12] As of October 2026, no final decision has appeared in the Federal Register. Which GLP-1s can be compounded follows that decision and the shortage history in more detail.

How to find out which kind of pharmacy filled your GLP-1

FDA notes that people who buy compounded drugs online “may not know the identity of the compounder that produced the drug.”^[4] You can usually find out in a few steps.

1. Read the vial and the pharmacy label. A 503B product must name the outsourcing facility, with its address and phone number, and say “This is a compounded drug.”^[9] A 503A label follows state rules; look for the name of the dispensing pharmacy. If the seller will not name the pharmacy, nothing else here can be checked.
2. Search the name on FDA’s outsourcing facility register. If it is there, the pharmacy is a 503B facility, and the register shows its last FDA inspection.^[3] Our pharmacy legitimacy lookup checks that register along with FDA warning letters and recalls in one search. Of the 68 pharmacies in the GLP Watchdog pharmacy register, 7 match FDA’s 503B register by name, city and state.
3. If it is not there, check the state license. Not being on the federal register is normal for a 503A pharmacy. 61 of the 68 pharmacies we track are not on it. The next step is the license lookup on the board of pharmacy website for the state where the pharmacy is located.^[4]
4. Notice “Office Use Only.” Federal law requires this phrase on 503B drugs that were not dispensed on a prescription for a named patient.^[9] A vial with that phrase that arrived at your home in your name should prompt a question to the seller.
5. Make sure the pharmacy actually exists and made the drug. FDA has found compounded semaglutide and tirzepatide with labels naming pharmacies that do not exist. It has also found labels naming real pharmacies that did not make the product.^[10] Call the pharmacy on the label using a number you find yourself, not the one on the vial.
6. Check enforcement history. FDA warning letters to GLP-1 sellers and pharmacies lists the letters that name compounded semaglutide or tirzepatide.

The same two-route system applies beyond GLP-1s. Peptides that are not components of an approved drug face the bulks-list rules described in are peptides legal. The prescription rules for each route are covered in whether compounded semaglutide needs a prescription.