Leucine Enkephalin (Leu-Enkephalin) vs N-Acetyl Semax
A neutral, side-by-side comparison of two nootropic & cognitive peptides — their mechanisms, dosing ranges, administration routes, side effects, and research evidence. For research and educational purposes only.
Leucine Enkephalin (Leu-Enkephalin)
One of the two primary endogenous enkephalins, alongside met-enkephalin. This pentapeptide (Tyr-Gly-Gly-Phe-Leu) acts primarily on δ-opioid receptors and secondarily on μ-opioid receptors. Research interests span pain modulation, neuroprotection, mood regulation, and immune system modulation. Extremely short half-life in vivo due to rapid enkephalinase degradation.
Full profileN-Acetyl Semax
N-Acetyl Semax is the acetylated form of Semax — an N-terminal acetyl group added to the standard Semax heptapeptide. The modification significantly improves resistance to aminopeptidases, extending the active half-life and producing a more sustained cognitive effect at lower doses. Considered by many researchers to be the preferred form of Semax for neurotrophin upregulation and focus enhancement.
Full profile| Leucine Enkephalin (Leu-Enkephalin) | N-Acetyl Semax | |
|---|---|---|
| Category | Nootropic & Cognitive | Nootropic & Cognitive |
| Also known as | Leu5-enkephalin, YGGFL, L-enkephalin, endogenous opioid pentapeptide | NA-Semax, Acetyl-Semax, N-Ac-MEHFPGP |
| Evidence | Research-stage | Research-stage |
| Dosing range | 0.1mg–1mg mg, Intranasal or SC; extremely short half-life requires frequent dosing or continuous delivery | 100mcg–600mcg mcg, Once daily (intranasal preferred) |
| Administration | Intranasal, Subcutaneous injection, Intraventricular (research only) | Intranasal (preferred), Subcutaneous injection |
| Key side effects | Tolerance development with repeated use (opioid receptor class effect), Mild euphoria (δ-opioid mediated), Nausea (at high doses), Constipation (opioid class effect at high doses) | Mild anxiety or over-stimulation at high doses, Nasal irritation (intranasal), Difficulty sleeping if dosed late in the day (more stimulating than standard Semax), Mild appetite suppression |
| Cited sources | 2 references | 2 references |
Key differences
- Administration: Leucine Enkephalin (Leu-Enkephalin) — Intranasal, Subcutaneous injection, Intraventricular (research only); N-Acetyl Semax — Intranasal (preferred), Subcutaneous injection.
- Dosing units differ: Leucine Enkephalin (Leu-Enkephalin) is dosed in mg, N-Acetyl Semax in mcg — they operate at different scales.
- Frequency: Leucine Enkephalin (Leu-Enkephalin) is typically Intranasal or SC; extremely short half-life requires frequent dosing or continuous delivery; N-Acetyl Semax is Once daily (intranasal preferred).
How each works
Leucine Enkephalin (Leu-Enkephalin)
Leu-enkephalin was one of the first endogenous opioid peptides characterized, following the discovery of opioid receptors in 1973. It preferentially activates δ-opioid receptors (DOR) over μ-opioid receptors (MOR), producing analgesia, modulation of GABA release, and reward pathway activation. Enkephalinase (neprilysin/NEP, CD10) cleaves the Gly-Phe bond within ~2 minutes IV, necessitating stable analogues or NEP inhibitors for research applications.
N-Acetyl Semax
Acetylation of the N-terminus blocks aminopeptidase cleavage at the most vulnerable site on the Semax molecule, extending its effective duration in biological fluids. Studies comparing acetylated vs non-acetylated ACTH fragment analogs consistently show greater stability and sustained receptor engagement with acetylated forms. N-Acetyl Semax demonstrates the same core BDNF/NGF upregulating and neuroprotective profile as Semax with reported greater potency per mcg due to improved bioavailability.
This comparison aggregates public research and structured profile data for informational purposes only. It is not medical advice and does not recommend either compound for human use. Consult a qualified healthcare provider before considering any peptide.