What it means
Section 503B was added to federal law in 2013 after a deadly outbreak tied to contaminated compounded injections. Facilities choose to register with the FDA, follow current good manufacturing practice rules and are inspected on a risk-based schedule.
Unlike 503A pharmacies, they can make drugs without a prescription for each patient, for example as stock for clinics. They also report the products they make to the FDA.
Stricter quality rules do not make their products FDA-approved. The FDA does not review 503B products for safety or effectiveness before they are sold, and copies of approved drugs are restricted unless the drug is on the FDA shortage list.
The FDA has warned some outsourcing facilities over repackaging unapproved GLP-1 ingredients, including retatrutide.
Why it matters
A 503B label signals stronger manufacturing standards, not FDA approval of the medicine inside.