Not medical advice. Talk to your provider before using any peptide.
Full disclaimerSemax vs Selank
Peptide Schedule Research TeamReviewed Apr 202617 Citations
Side-by-side comparison of dosage, benefits, and side effects.
226 PubMed citations and a prescription approval in Russia. That track record separates Semax (Met-Glu-His-Phe-Pro-Gly-Pro, ACTH 4-10 analog) from most peptides in the nootropic category. The mechanism is centered on BDNF. Dolotov and colleagues confirmed that a single Semax injection at 50 mcg/kg produced a 3-fold increase in BDNF mRNA and a 1.4-fold increase in BDNF protein in the rat hippocampus (PMID 16996037). A separate group showed binding-specific increases in BDNF protein in the basal forebrain (PMID 16635254). Beyond neurotrophins, Semax activates dopaminergic and serotonergic systems without touching cortisol, unlike its parent molecule ACTH. In practice, the community doses 300 to 600 mcg intranasally each morning for 10 to 14 days. Thousands of user reports across r/Peptides, r/nootropics, and Longecity describe improved focus, verbal fluency, and working memory starting within the first few days. The Selank stack (300 mcg of each, intranasal AM) is the most popular combination, adding anxiolytic balance to the dopaminergic stimulation. Lebedeva and colleagues tracked 110 stroke patients on Semax and confirmed increased plasma BDNF. A 2025 study in transgenic Alzheimer's mice showed reduced amyloid plaques (PMID 41479572). Another 2025 paper in the British Journal of Pharmacology identified a new mu-opioid receptor mechanism for spinal cord injury recovery (PMID 40692165). The science is expanding, but it still leans heavily on animal models and small Russian clinical samples. No placebo-controlled RCT has been run in healthy adults at any dose.
View full guide →A 192-patient randomized trial tested this peptide head-to-head against medazepam for generalized anxiety disorder and found comparable anxiolytic effects (Zozulya et al. 2008, PMID 18454096). A second study compared it directly to phenazepam with similar results and a cleaner side effect profile (PMID 25176261). That level of clinical evidence puts Selank ahead of most research peptides. Selank (full sequence: Thr-Lys-Pro-Arg-Pro-Gly-Pro) is a synthetic heptapeptide analog of tuftsin, developed at the Institute of Molecular Genetics of the Russian Academy of Sciences. Its mechanism hits multiple pathways at once. It inhibits enkephalinase, which extends the half-life of your body's own enkephalins. It modulates GABA receptor expression (confirmed at the gene level in PMID 26847159). And it influences serotonin pathways and upregulates BDNF. The practical result is an anxiolytic that doesn't sedate you or dull your thinking. Users across dozens of Reddit threads on r/peptides and r/Nootropics describe it as "taking the edge off" while leaving focus intact. The most common protocol mirrors Russian clinical trial design: 250 to 500 mcg daily for 2 to 4 weeks, then cycling off for an equal period. Intranasal delivery has become the community's preferred route for its faster onset (15 to 30 min) and convenience. Two honest caveats: every published clinical trial originates from Russian academic institutions, with no independent Western replication to date. And the plasma half-life is very short (roughly 2 to 3 minutes IV), which means the mechanism behind its prolonged effect still isn't fully explained. The FDA removed Selank acetate from the Category 2 bulks list in September 2024; it remains research-only in the US.
View full guide →At a Glance
| Attribute |  Semax |  Selank |
|---|---|---|
| Category | Cognitive | Cognitive |
| Safety Grade | B | B |
| Half-Life | ~2-3 min (IV) | ~2-3 min (IV) |
| Route | Subcutaneous or Nasal | Subcutaneous or Nasal |
| Vial Sizes | 5mg | 5mg |
| Beginner Dose | 200mcg Daily | 250mcg Daily |
| Moderate Dose | 500mcg Daily | 500mcg Daily |
| Aggressive Dose | 1000mcg Daily | 750mcg Daily |
| Dosing Source | Community | Community |
| Side Effects | Sleep disruption is the most consistently reported problem, and it is almost always a timing error. Semax increases dopamine turnover. Dosing after noon delays sleep onset for hours. Restricting administration to before 10 AM resolves the issue for most users. Even a 2 PM dose can wreck that night's sleep architecture. Anxiety and irritability rank second. The effect is dose-dependent. At 600 mcg per day and above, community reports of agitation, frustration with interruptions, and generalized anxiety increase sharply. Users with pre-existing anxiety disorders face the highest risk. Reducing the dose by 50% typically resolves the issue within 1 to 2 days. Stacking with Selank 300 mcg mitigates anxiety for most users; that combination is the most popular community protocol for exactly this reason. Nasal irritation affects intranasal users during the first week. Mild burning, tingling, and dryness at the mucosal surface are common and generally self-limiting. A saline rinse between doses helps. For persistent irritation, switching to subcutaneous injection eliminates the local effect entirely. Afternoon fatigue and a "comedown" feeling appear at doses of 600 mcg per day and higher. Splitting the dose into 2 administrations (morning and before 1 PM) or reducing to 300 to 400 mcg often solves this. Emotional blunting or mental flatness is reported with sustained use above 600 mcg per day beyond day 14. A minority of users running extended high-dose cycles also report reduced libido. Both effects resolve after stopping. Hair thinning has been described at very high doses over long periods. The reports are rare and uniformly described as reversible. Melanocortin receptor (MC4R) activation is the speculated mechanism. Human safety data is limited. The published literature comes from Russian clinical trials in stroke and cognitive disorder patients, not healthy adult nootropic users. No formal adverse event reporting exists for the community dosing context. Contraindications: pregnancy or breastfeeding (no safety data), known hypersensitivity to ACTH-derived peptides, active intracranial hypertension, history of seizure disorders (limited data, use with caution), and children under 18 without physician supervision. SSRIs and SNRIs require monitoring because Semax modulates serotonin systems; additive serotonergic effects are possible. Dopaminergic drugs (L-DOPA, dopamine agonists) carry additive stimulation risk; dose adjustment may be needed. Stop use and consult a physician if anxiety persists despite morning-only dosing at 300 mcg or below, if sleep disruption does not resolve with timing changes, or if blood pressure exceeds 130/80 mmHg. | The most important safety concern with Selank is its interaction profile, not the peptide itself. Selank modulates GABA receptor expression, serotonergic pathways, and enkephalin metabolism simultaneously. Combining it with benzodiazepines risks excessive CNS depression. Adding it to an SSRI or SNRI creates additive serotonergic activity; watch for agitation, tremor, and diaphoresis. If you're on immunosuppressive therapy (cyclosporine, tacrolimus, methotrexate), Selank's tuftsin-derived immunomodulatory effects may interfere with your intended immunosuppression. On its own, the side effect profile is remarkably clean. The 192-patient GAD trial (PMID 18454096) and the phenazepam comparison (PMID 25176261) reported fewer adverse events than the active comparators. No sedation. No addiction potential. No withdrawal syndrome has been documented in any published study. What users actually report: the most common complaint is nasal stinging or irritation at higher intranasal doses (400 to 600 mcg per administration). Diluting with more bacteriostatic water or splitting the dose across both nostrils reduces this. Mild fatigue during the first one or two doses is occasionally mentioned but typically resolves quickly. Batch-to-batch inconsistency from unregulated research vendors is the number one cause of "non-response" in community reports; that's a sourcing problem, not a pharmacological one. The effect is too subtle for acute panic. Selank is a background anxiolytic, not a rescue medication. If you're expecting benzodiazepine-level sedation on demand, you'll be disappointed. By design, the effect ceiling is lower. All published clinical data comes from Russian institutions. Total human trial exposure is limited to the study populations described above. No long-term safety data beyond trial durations (typically 2 to 4 weeks) exists. Pregnancy and breastfeeding are absolute contraindications due to insufficient safety data. Children under 18 have not been studied. Active autoimmune conditions may be affected by Selank's immunomodulatory properties. Practical stop signals: discontinue if you experience paradoxical anxiety increase, any hypersensitivity reaction (rash, itching), or signs of excessive serotonergic activity when combined with other medications. Consult a physician before combining Selank with any CNS-active medication. |
Key Differences
- Semax powerfully increases BDNF for learning and neuroplasticity; Selank modulates serotonin and GABA for anxiolytic effects.
- Semax is more stimulating and focus-oriented; Selank is calming and anti-anxiety without sedation.
- Both are available as nasal sprays for needle-free use.
- Semax is better for acute cognitive tasks; Selank is better for sustained calm focus and stress resilience.
When to Choose Semax
- Your primary goal is enhanced learning, memory, and focus
- You want increased BDNF for neuroplasticity
- You need acute mental performance (studying, work sprints)
- Cognitive decline prevention is a priority
When to Choose Selank
- Anxiety reduction without sedation is your primary goal
- You want calm, sustained focus rather than stimulation
- Stress resilience and emotional regulation are priorities
- You prefer a more gentle cognitive enhancer
Can You Stack Semax + Selank?
Semax + Selank is the classic nootropic peptide stack. Semax provides the cognitive boost while Selank keeps anxiety in check: complementary mechanisms without interference.
Dosage Calculators
Or use the universal Peptide Calculator for any peptide.