Glossary: the terms on this site, defined

Terms are grouped by where you will meet them. Each definition is the working meaning used on this site; where a term has a legal definition, the source is FDA's page linked in the sources.

Regulatory

503A. The section of the Food, Drug, and Cosmetic Act under which a licensed pharmacy may compound a drug for an identified patient on a prescription, using bulk substances that meet one of three conditions: a USP or NF monograph, being a component of an FDA-approved drug, or appearing on the 503A bulks list. See the 503A bulks list explained.

503B. The section covering outsourcing facilities, which may compound larger batches without patient-specific prescriptions under FDA registration and inspection, using bulk substances on a separate 503B list. Ipamorelin's Category 2 listing is under the 503B interim policy.

Bulk drug substance. The active pharmaceutical ingredient as a raw material, before it is made into a finished drug.

503A bulks list. The list FDA develops by regulation of bulk substances that may be used in 503A compounding despite having no monograph and being in no approved drug. Substances reach it by final rule only.

Category 1, 2, 3. FDA's interim sorting of substances nominated for the 503A bulks list. Category 1: nominated with sufficient information, under evaluation, FDA does not intend to act against compounders using it if other conditions are met. Category 2: significant safety risks identified; FDA may act. Category 3: nominated with insufficient information. Substances nominated on or after January 7, 2025 are not categorised.

Nominated but withdrawn. FDA's table on the Category 2 page of substances whose nominations were withdrawn or moved to committee review. FDA keeps its safety concern beside each. Not Category 1, not the list.

PCAC. The Pharmacy Compounding Advisory Committee, twelve voting members who advise FDA on which nominated substances should be listed. Its votes are recommendations. FDA is not bound by them.

Final rule. The Federal Register document that changes the regulation and adds a substance to the list. The only step that changes what a pharmacy may lawfully use.

Approved drug; label. A drug reviewed and approved by FDA under a New Drug Application (NDA) or Biologics License Application (BLA). Its label (prescribing information) is the FDA-reviewed document stating indication, dose, warnings, adverse-reaction rates and storage. Labels live on DailyMed. See tesamorelin and PT-141.

Component of an approved drug. One of the three 503A routes. Tesamorelin and bremelanotide qualify because Egrifta and Vyleesi exist. A compounded copy is still not the approved product.

Essentially a copy. A 503A limit: a pharmacy may not regularly compound what is essentially a copy of a commercially available drug. Explained on the compounding site.

Research use only (RUO). A label on chemicals sold for laboratory use, with no claim to identity, sterility or potency for human use and no pharmacy, prescription or FDA involvement. Most peptides sold online carry it. See salt forms and research use only.

Beyond-use date (BUD). The date after which a compounded preparation must not be used, assigned by the compounding pharmacy under USP standards. See storage and handling and the countdown tool.

Excursion. A temporary departure from the labelled storage temperature. Approved labels state what is permitted; for a compounded preparation only the pharmacy can say.

Research

RCT. Randomised controlled trial: participants are assigned by chance to the intervention or a comparator. Randomisation is what balances the unknowns between groups.

Placebo-controlled. The comparator is an inactive look-alike. Distinguishes the drug's effect from expectation and time. An active-comparator trial (drug vs another drug) without placebo cannot do this; see selank.

Double-blind. Neither participant nor assessor knows the assignment. Protects against biased reporting and assessment.

Open-label. Everyone knows who received what. Common in extensions and pilots; weak for subjective endpoints.

Phase 1, 2, 3. Roughly: safety and dosing in small groups, usually healthy volunteers (1); efficacy signal and dose in patients (2); confirmatory trials large enough to support approval (3). Several substances on this site stopped at phase 1 or failed at phase 2.

Primary endpoint. The single pre-specified outcome a trial is designed to test. A trial that misses it has not shown efficacy, whatever the secondary endpoints do. See ipamorelin.

Treatment effect. The difference between groups, usually with a confidence interval. Tesamorelin's phase 3 treatment effect on visceral fat was -15.4%.

p-value. The probability of a result at least this extreme if there were no true difference. Below 0.05 is the conventional threshold; p = 0.15 is not significant.

n. Number of participants. Two people is a case report, not a safety study.

Case series; chart review; pilot. Uncontrolled human reports. They generate hypotheses. On this scale they are grade D evidence.

Systematic review. A review that searches the literature by a stated method and reports what it found and excluded. The 2025 BPC-157 review that found 35 preclinical studies and 1 clinical is one.

Preclinical. Animal or cell studies. In vitro means in a dish; in vivo means in a living organism, which on peptide pages almost always means a rat.

Proxy molecule. Our term for a related but different compound whose studies are cited as if they applied: thymosin beta-4 for TB-500, epithalamin for epitalon, nicotinamide riboside for NAD+. Shown in tables, excluded from grades.

Immunogenicity. The tendency of a substance to provoke an immune response, including anti-drug antibodies. Measured for approved biologics and peptides (the tesamorelin label reports 50% at 26 weeks) and, per FDA, unmeasured for every research peptide it has flagged.

Peptide-related impurities; API characterisation. Truncated, oxidised or aggregated forms of the peptide, and the analytical work needed to know what is in the vial. FDA's recurring concern on the Category 2 page.

Aggregation. Peptide molecules clumping together, which raises immunogenicity risk and is sensitive to storage, light and handling.

Half-life. Time for the blood concentration to fall by half. Ipamorelin, about 2 hours; CJC-1295, 5.8 to 8.1 days. Matters for how long an adverse effect persists after the last dose.

Site terms

Grade A to D; X flag. This site's scale for the kind of human evidence that exists for a stated use, and the flag for a published FDA safety concern. Defined in full on the methodology page.

Graded for. The specific use a grade applies to. Grades do not transfer to other uses.

Content current as of. The date FDA stamps on its pages. We quote it because status changes and the date is the status.