Leucine Enkephalin (Leu-Enkephalin) vs 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 profileSemax
Semax is a synthetic heptapeptide derived from adrenocorticotropic hormone (ACTH) — specifically the 4–7 fragment modified with a C-terminal Pro-Gly-Pro extension for stability. Developed in Russia in the 1980s and used clinically there for stroke recovery, cognitive enhancement, and neuroprotection, it is one of the most researched nootropic peptides with a decades-long safety record in Eastern European clinical practice. Its primary mechanism involves potent upregulation of BDNF (Brain-Derived Neurotrophic Factor).
Full profile| Leucine Enkephalin (Leu-Enkephalin) | Semax | |
|---|---|---|
| Category | Nootropic & Cognitive | Nootropic & Cognitive |
| Also known as | Leu5-enkephalin, YGGFL, L-enkephalin, endogenous opioid pentapeptide | ACTH(4-7)PGP, Met-Glu-His-Phe-Pro-Gly-Pro |
| Evidence | Research-stage | Investigational (in trials) |
| Dosing range | 0.1mg–1mg mg, Intranasal or SC; extremely short half-life requires frequent dosing or continuous delivery | 200mcg–900mcg mcg, Once or twice daily (intranasal most common) |
| Administration | Intranasal, Subcutaneous injection, Intraventricular (research only) | Intranasal (preferred — high CNS bioavailability), 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 restlessness at high doses, Nasal irritation (intranasal route), Increased energy / difficulty sleeping if dosed too late in the day, Mild appetite suppression |
| Cited sources | 2 references | 3 references |
Key differences
- Evidence level differs: Leucine Enkephalin (Leu-Enkephalin) is research-stage, while Semax is investigational (in trials).
- Administration: Leucine Enkephalin (Leu-Enkephalin) — Intranasal, Subcutaneous injection, Intraventricular (research only); Semax — Intranasal (preferred — high CNS bioavailability), Subcutaneous injection.
- Dosing units differ: Leucine Enkephalin (Leu-Enkephalin) is dosed in mg, 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; Semax is Once or twice daily (intranasal most common).
- Research depth: this profile cites 2 sources for Leucine Enkephalin (Leu-Enkephalin) vs 3 for Semax.
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.
Semax
Semax increases BDNF expression in the hippocampus and frontal cortex by 1.3–1.6x at research doses in rodent models. It also upregulates NGF (nerve growth factor) and modulates serotonin, dopamine, and NMDA receptor systems. Russian clinical data (not yet replicated in Western trials) suggests efficacy in ischemic stroke recovery, ADHD, glaucoma, and cognitive decline. The Pro-Gly-Pro C-terminal extension dramatically improves resistance to enzymatic degradation compared to native ACTH(4-7).
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.