Neuropeptides

What defines a neuropeptide

A neuropeptide is defined by where it comes from and how it is released, not by one shared structure. Neurons package neuropeptides into dense-core vesicles and release them through the regulated secretory pathway, and they act on neural targets [R1]. Most act on G protein-coupled receptors. Oxytocin is the textbook case: it is made mainly in magnocellular neurons of the hypothalamic paraventricular and supraoptic nuclei, and its receptor is a class I G protein-coupled receptor coupled mainly through G_q to phospholipase C-β [R2].

Two compounds here are synthetic analogues, not natural brain peptides. Semax joins the ACTH(4–7) fragment (Met-Glu-His-Phe) to a Pro-Gly-Pro tail [R3]. Selank joins tuftsin (Thr-Lys-Pro-Arg) to the same Pro-Gly-Pro tail [R4]. DSIP was first isolated from rabbits in 1977; no gene, precursor or receptor for it has been identified [R5] [R6]. For a side-by-side look at the two heptapeptides, see Semax vs Selank.

Compounds in this category

Identity data: FDA GSRS/UNII records (Semax I5FAL2585H, Selank TS9JR8EP1G, emideltide YN28Z5YZ73, oxytocin 1JQS135EYN) and KEGG D00089 for oxytocin [R9]. MW is the average molecular weight of the free peptide, calculated from the formula (KEGG value for oxytocin); salt forms weigh more.

Regulatory status

Only oxytocin is an FDA-approved drug: oxytocin injection is a prescription product approved under NDA 018261 for antepartum and postpartum use [R10]. Our research vial is not that product. Semax, Selank and DSIP are not approved drugs in the US. Selank's 503A nomination was withdrawn and it left FDA's Category 2 list on September 27, 2024 [R11]. Semax and DSIP were among 12 peptides FDA said on April 15, 2026 it would remove from Category 2 [R12]. On July 24, 2026, FDA's advisory committee voted 8–5–1 to recommend Semax for the 503A bulks list and 6–7–1 against DSIP; these votes are advisory, and FDA rulemaking is still needed [R13]. None of this makes a research-labeled vial an approved product. See RUO peptides explained.

Frequently asked questions

What are neuropeptides?

Neuropeptides are small protein-based signaling molecules that neurons make and release through the regulated secretory pathway. Close to 70 mammalian genes encode their precursors [R1].

Are Semax and Selank natural neuropeptides?

No. Both are synthetic heptapeptides. Each adds a Pro-Gly-Pro tail to a shorter natural fragment: ACTH(4–7) for Semax and tuftsin for Selank [R3] [R4].

Does DSIP have a known receptor?

No. A 2006 review notes that no gene, precursor protein or receptor for DSIP has been isolated [R6].

Is oxytocin an approved drug?

Yes. Oxytocin injection is FDA-approved for prescription obstetric use [R10]. The research-grade oxytocin sold here is not an approved drug product and is for laboratory use only.

How do I check a batch?

Each product page has a batch Certificate of Analysis with HPLC purity and mass-spec identity. Our guide How to read a peptide COA explains each line.

References

1. Burbach JPH. What are neuropeptides? Methods Mol Biol. 2011;789:1–36. doi:10.1007/978-1-61779-310-3_1. PMID 21922398.
2. Gimpl G, Fahrenholz F. The oxytocin receptor system: structure, function, and regulation. Physiol Rev. 2001;81(2):629–683. doi:10.1152/physrev.2001.81.2.629. PMID 11274341.
3. FDA Global Substance Registration System. SEMAX, UNII I5FAL2585H. precision.fda.gov/uniisearch/srs/unii/I5FAL2585H.
4. FDA Global Substance Registration System. SELANK, UNII TS9JR8EP1G. precision.fda.gov/uniisearch/srs/unii/TS9JR8EP1G.
5. Schoenenberger GA, Monnier M. Characterization of a delta-electroencephalogram (-sleep)-inducing peptide. Proc Natl Acad Sci USA. 1977;74(3):1282–1286. doi:10.1073/pnas.74.3.1282. PMID 265572.
6. Kovalzon VM, Strekalova TV. Delta sleep-inducing peptide (DSIP): a still unresolved riddle. J Neurochem. 2006;97(2):303–309. doi:10.1111/j.1471-4159.2006.03693.x. PMID 16539679.
7. Dolotov OV, Karpenko EA, Inozemtseva LS, et al. Semax, an analog of ACTH(4–10) with cognitive effects, regulates BDNF and trkB expression in the rat hippocampus. Brain Res. 2006;1117(1):54–60. doi:10.1016/j.brainres.2006.07.108. PMID 16996037.
8. Volkova A, Shadrina M, Kolomin T, et al. Selank administration affects the expression of some genes involved in GABAergic neurotransmission. Front Pharmacol. 2016;7:31. doi:10.3389/fphar.2016.00031. PMID 26924987.
9. KEGG DRUG. D00089 Oxytocin. kegg.jp/entry/D00089.
10. US FDA. Oxytocin injection, USP prescribing information, NDA 018261 (label posted to Drugs@FDA, 2021). accessdata.fda.gov.
11. Reed Smith. FDA removes certain peptide bulk drug substances from Category 2 of interim 503A bulks list and sets dates for PCAC review. Client Alert 2024-208 (October 2024). reedsmith.com.
12. Frier Levitt. FDA to remove 12 popular peptides from the Category 2 "do not compound" list (April 16, 2026). frierlevitt.com.
13. McDermott Will & Schulte. Bulk list bound? PCAC backs majority of peptides in two-day public meeting (July 27, 2026). mcdermottlaw.com.

For laboratory research use only. Not for human or veterinary use.