Semax + Selank subq: together or apart?

A question that surfaces regularly in peptide research forums: if someone is using both Semax and Selank subcutaneously, should they be administered at the same time or separated by a gap? The honest answer is that no human clinical trial has tested the two compounds together, and no published pharmacokinetic study directly compares simultaneous versus sequential subcutaneous dosing of this pair.

This article lays out what the peer-reviewed literature says about each peptide individually, what is known about their mechanisms, and what that implies for administration timing. It is not dosing advice. Decisions about whether to use either compound at all belong with a clinician who knows your medical history.

What Semax and Selank are

Semax is a synthetic heptapeptide with the amino acid sequence Met-Glu-His-Phe-Pro-Gly-Pro. It was designed at the Institute of Molecular Genetics of the Russian Academy of Sciences as a stable analogue of the ACTH(4-7) fragment, with a Pro-Gly-Pro tail appended to slow enzymatic breakdown. Its molecular formula is C37H51N9O10S, with a molecular weight of approximately 813.9 g/mol^[1]. In Russia it is a licensed prescription nasal spray, registered under the country's Vital and Essential Drugs list since 2011^[2]. It has no marketing authorisation in the EU, EEA, UK or US.

Selank is also a synthetic heptapeptide, with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro. It was developed as a stable analogue of tuftsin, a tetrapeptide naturally produced by the spleen. The Pro-Gly-Pro extension it shares with Semax was added to resist the same carboxypeptidase and prolyl endopeptidase enzymes that degrade shorter peptides rapidly. Selank's molecular formula is C33H57N11O9, with no sulfur-containing residues^[3]. Like Semax, it is a registered prescription medicine in Russia and has no marketing authorisation in the EU, EEA, UK or US.

How they act on the brain

The two peptides have distinct but partly overlapping mechanisms. Semax modulates monoaminergic signalling: animal research by Eremin and colleagues (2005) found that Semax increased striatal serotonin metabolite levels by approximately 25% within two hours and amplified dopaminergic responses when combined with amphetamine^[4]. Separately, Dolotov and colleagues (2006) showed that intranasal Semax raised brain-derived neurotrophic factor (BDNF) protein in the rat basal forebrain within three hours at doses of 50 to 250 mcg/kg, and demonstrated specific binding to membrane receptors with a dissociation constant of approximately 2.4 nanomolar^[5]. A 2025 study in the British Journal of Pharmacology identified a mu-opioid receptor (Oprm1) pathway through which Semax promotes neuroprotection in a mouse spinal cord injury model^[6].

Selank's anxiolytic profile is better characterised mechanistically than Semax's. Vyunova and colleagues (2018) showed that Selank acts as a positive allosteric modulator at GABA-A receptors, increasing GABA binding without the same direct receptor activation that drives benzodiazepine dependence^[7]. Semenova and colleagues (2009) found that Selank enhanced serotonin metabolism in the rat brain stem within 30 minutes of administration, complementing its GABAergic activity^[8]. Inozemtseva and colleagues (2008) reported that intranasal Selank also regulates BDNF expression in the rat hippocampus^[9], a finding that parallels Semax's own BDNF-related effects in the basal forebrain.

In practice, both peptides modulate BDNF and serotonin-related signalling, though through different receptor targets and in different brain regions. Whether those effects add together, work independently, or interfere with each other in a living system has not been studied.

The subcutaneous route: what the literature shows

The Russian licensed form of Semax is an intranasal nasal spray. The published clinical study by Gusev and colleagues (2018), which used Semax in 110 ischemic stroke patients, also used the intranasal route at 6,000 mcg/day over two 10-day courses^[2]. Similarly, Dolotov's BDNF work used intranasal delivery, and Inozemtseva's Selank BDNF paper used intranasal administration in rats^[5][9]. There is no published pharmacokinetic study comparing intranasal and subcutaneous administration of Semax or Selank in humans.

Subcutaneous administration has appeared in preclinical and researcher-community use, but published human pharmacokinetic data for either compound via the subcutaneous route are absent from the peer-reviewed literature as of this writing. The grey-market community discussion around subcutaneous use of these peptides is largely extrapolation from the intranasal literature and general peptide pharmacokinetics, not from direct human comparative studies.

The timing question: what can be reasoned from pharmacology

Because no head-to-head timing study exists, any position on concurrent versus sequential subcutaneous dosing of Semax and Selank rests on inference from their individual mechanisms. The following represents the published literature's implications, not established clinical guidance.

The argument for concurrent administration is simple: both peptides are heptapeptides with the same Pro-Gly-Pro stabilising tail, both have very short plasma half-lives in general (small peptides are rapidly cleaved by circulating peptidases), and their receptor targets appear to be distinct enough that direct pharmacokinetic competition at the injection site is unlikely. The two compounds do not appear to bind the same receptor. Semax's primary interactions involve BDNF upregulation, monoaminergic signalling, and Oprm1^[4][6]. Selank's primary interaction involves GABA-A positive allosteric modulation and serotoninergic metabolism^[7][8]. Administering them at the same site in the same injection would likely mix the two peptides in the subcutaneous tissue, but they would then be absorbed into systemic circulation and cross the blood-brain barrier independently.

The argument for separating them is more cautious: the combined effect on serotonin and BDNF in the same acute window is unknown in humans, the GABA-A modulation from Selank alongside Semax's dopaminergic and serotoninergic activity has not been characterised together, and separate administration makes it easier to attribute any response or adverse effect to one compound rather than the other.

Neither argument is supported by a controlled clinical study. The absence of data is the main finding here.

Regulatory and safety framing

Both Semax and Selank lack marketing authorisation in any country in the site's coverage area outside Russia. Subcutaneous use of either compound falls outside the scope of any approved indication anywhere covered by this site. The grey-market research-peptide supply chain for both compounds has no regulatory oversight in the EU, EEA, UK or US, meaning product identity, purity, sterility, and potency cannot be verified through any official channel. Independent testing of grey-market peptide products as a category consistently finds purity and identity failures across the field. For more on the specific supply risks for Semax, see grey-market risks for Semax.

This article is for informational and educational purposes only. It does not constitute medical advice, a dosing recommendation, or an endorsement of using either compound. Anyone considering any peptide should consult a qualified healthcare provider.