Two different things get called compounded
Compounded medication comes from one of two very different kinds of facility, and which one made your vial matters more than almost anything else on the label.
A 503A pharmacy compounds against an individual prescription for an individual patient. It is regulated primarily by state boards of pharmacy. A 503B outsourcing facility registers with the FDA, makes larger batches, and is subject to federal inspection and current good manufacturing practice requirements. Both are legal. They are not equivalent, and telehealth services rarely volunteer which one they use.
Compounded drugs are not approved drugs
This is definitional rather than an accusation. A compounded preparation has not been reviewed by the FDA for safety, for efficacy, or for manufacturing quality before it reaches you. Compounding exists for good reasons: an allergy to an excipient in the commercial product, a dose nobody manufactures, a patient who cannot use the available presentation.
What compounding is generally not permitted to be is a copy of a commercially available approved drug. That restriction is the whole story of the last two years in this category. While a drug sits on the FDA shortage list, compounders may make copies of it. Semaglutide and tirzepatide were both on that list through 2023 and 2024, which is why compounded GLP-1s became widely available. Both shortages have since been declared resolved, and the legal grounding narrowed accordingly.
What is actually different in the vial
- Active ingredient form. The approved products use a specific form of the molecule. Material sold as semaglutide sodium or semaglutide acetate is a salt form and is not the approved active ingredient. The FDA has said so directly.
- Presentation. Brand medication arrives in fixed-dose pens. Compounded medication usually arrives as a multi-dose vial at a concentration the pharmacy chose, which you draw yourself.
- Preservatives. A multi-dose vial needs a preservative to be used over weeks. A single-use pen does not. This is a genuine formulation difference, not a corner cut.
- Additives. Some compounded preparations include B12 or other ingredients. No evidence supports that improving outcomes, and it makes attributing a side effect to a cause harder.
What is different in oversight
An approved product carries batch testing, facility inspection, a recall mechanism and an adverse event reporting system that regulators actually watch. When something goes wrong at scale, there is machinery to catch it.
For a compounded preparation, how much of that exists depends almost entirely on which kind of facility made it. This is why the 503A or 503B question is the most useful one you can ask, and why an evasive answer to it is itself an answer.
What is different in practice
- Dose flexibility. A vial can be drawn at any dose. Pens cannot. For people who do better on intermediate or very low doses, this is a real clinical advantage and not only a cost one.
- Price. The gap between compounded and brand cash pricing is several-fold. It is the reason the category exists at the scale it does.
- Supply continuity. Brand availability moves with manufacturing capacity. Compounded availability moves with regulatory status, which can change faster and with less warning.
- Dosing error risk. Drawing your own dose from a vial at a concentration you have to convert is where ten-fold errors happen. Pens remove that failure mode entirely.
The questions that settle it
- Is the medication compounded at a 503A pharmacy or a 503B outsourcing facility, and what is its name?
- Is there a certificate of analysis from an independent laboratory, tied to the batch I am receiving?
- Is this the base form of the molecule, or a salt form?
- What concentration is the vial, and what syringe should I use for my dose?
- What happens to my treatment if compounded supply becomes unavailable?
The honest summary
Compounded medication is cheaper, more flexible on dose, and carries less assurance about what is in the vial and who checked. Brand medication is expensive, inflexible, and about as certain as pharmaceutical supply gets.
Neither of those is the right answer for everyone. What is not defensible is choosing between them without knowing that is the trade you are making.
Sources
- FDA guidance on compounding under sections 503A and 503B of the FD&C Act
- FDA statements on compounded semaglutide and salt forms
- FDA drug shortage database