Class
These are peptides that act on immune function rather than on a metabolic or structural target: one an endogenous antimicrobial peptide the body makes at every barrier surface, the other a thymic peptide that participates in T-cell maturation. Neither has a lawful United States route, and the reasons differ in an instructive way.
One carries a substantial controlled-trial literature accumulated outside the United States and was refused by an advisory committee that read it. The other carries a trial count that looks large and is almost entirely a record of the body's own peptide being measured rather than a drug being given.
Molecules in this class
| Molecule | Class | US status | Position |
|---|---|---|---|
| LL-37Cathelicidin LL-37; hCAP18 | Immune peptides | No lawful route | Nomination withdrawn in 2026; on no list. FDA's safety finding cites nonclinical evidence of harm to male reproduction and of pro-tumorigenic effects in some tissues. |
| Thymosin alpha-1Thymalfasin; Ta1 | Immune peptides | Nomination withdrawn | Licensed as a medicine in other countries and never approved here; the advisory committee voted 4–17 against listing it in December 2024, and the nomination was withdrawn. |
Cathelicidin LL-37; hCAP18
Nomination withdrawn in 2026; on no list. FDA's safety finding cites nonclinical evidence of harm to male reproduction and of pro-tumorigenic effects in some tissues.
Thymalfasin; Ta1
Licensed as a medicine in other countries and never approved here; the advisory committee voted 4–17 against listing it in December 2024, and the nomination was withdrawn.
The measured cases are at LL-37, where sixty-eight of seventy-two trial-type records administer nothing, and thymosin alpha-1, refused 4 to 17 by the committee that reviewed it. The human trial record prints both counts with the searches behind them.
Reference tables
Definitions