Semax/Selank blend: the dosing math gap

A reader on r/peptides asked a version of a question that comes up constantly about blended products: how much bacteriostatic water to add to a Semax/Selank blend vial, and how many units to draw on an insulin syringe. There is no defensible number to give here, and it is not because reconstitution math is some guarded secret. The formula itself is public, and an approved peptide drug's own label spells it out in exact figures^[1]. The problem is that a blend vial removes the one input that formula needs: how much of each peptide is actually inside it.

The reconstitution formula is not the hard part

Reconstituting a peptide means dissolving freeze-dried powder in a diluent, usually bacteriostatic water, until it reaches a known concentration, expressed in milligrams per milliliter. From there, an insulin syringe marked in units does the rest of the conversion: a standard U-100 syringe is calibrated so that 100 units equals 1 milliliter, so drawing a given volume at a known concentration delivers a known mass. None of that is hidden information. Tesamorelin, sold as Egrifta WR and one of the few peptide drugs with full FDA approval, publishes the exact numbers on its own label: reconstitute one vial with 1.3 mL of diluent to reach 8 mg per mL, then draw 0.16 mL, which is 16 units on a U-100 syringe, for the approved 1.28 mg daily dose^[1]. That is what a transparent reconstitution instruction looks like once a manufacturer has tested it and a regulator has reviewed it. See our tesamorelin page for the approved indication that instruction supports.

What a blend vial does not tell you

A Semax/Selank blend sold online is a different kind of product. Even when a listing states a combined weight, for example a '10 mg blend', that figure describes the vendor's claim about total peptide content, not a regulator-verified split between two active substances. Without a verified milligram figure for the Semax and a separate verified milligram figure for the Selank, the concentration step in the formula above cannot be completed correctly for either compound, because the math needs the mass of the specific substance being dosed, not the mass of the vial's declared total. Neither peptide has an authorized medicine to check a vendor's claim against: a search of the EU Clinical Trials Register returns zero results for 'semax'^[3] and zero for 'selank'^[4], and outside Russia both circulate through unregulated research-chemical channels rather than a pharmacy with batch testing behind it. Our Semax page and our Selank explainer cover that regulatory gap for each compound in more detail.

The published dosing figures do not transfer either

Even a reader who trusted a vendor's stated ratio would run into a second problem: the human dosing data that exists for Semax was never generated for an injectable blend. The most-cited figure, from Gusev and colleagues' 2018 study of 110 ischemic stroke patients, used a regimen of 6,000 micrograms per day across two 10-day courses^[5], and the compound's research base, including the rat studies that established its effect on brain-derived neurotrophic factor, delivers it intranasally, as a nasal spray, not by injection^[6]. A number generated for a licensed nasal spray used in stroke rehabilitation does not convert into a syringe-unit figure for a differently manufactured injectable blend used by a healthy person. There is no published human study of an injected Semax/Selank combination to draw a number from instead.

Guessing here has a documented failure mode

Unit confusion of exactly this kind is not hypothetical. In 2024 the FDA issued an alert after receiving reports tied to compounded injectable semaglutide, another peptide-class drug, in which patients drew up five to twenty times their intended dose, tracing the errors to confusion between milliliters, milligrams and 'units', plus unfamiliarity with measuring a dose from a multidose vial^[2]. That alert involved a single, well-characterized compound with a stated concentration. A blend of two unregulated peptides at an unverified ratio removes the one fixed point, a known concentration, that even that better-documented failure still had. A separate, more basic safety rule applies to any vial that gets drawn from repeatedly: the CDC's injection-safety guidance is one needle, one syringe, one time, and it directs against entering a medication vial with a syringe or needle that has already been used^[7].

What this is not

This is not a claim that reconstitution math is dangerous knowledge that should stay hidden. The Egrifta WR label above shows exactly what a transparent version looks like, published for anyone to read. Nor is this a verdict on whether Semax or Selank, individually, could do anything useful for a given person. What it describes is a specific gap: for a blended, unregulated, injectable product with an unverified per-peptide content, there is no defensible way to complete the concentration math the original question is actually asking for, and no published clinical study to substitute for it.

Why this matters

If you already have a blend vial and are trying to work out how much bacteriostatic water to add or how many units to draw, a pharmacist can check what is actually achievable with the information available, and a clinician can weigh whether using it at all makes sense given your history. Neither of those conversations can happen over a forum thread. This article is educational and journalistic. It does not provide reconstitution, dosing or injection instructions for this or any other product, and it is not a substitute for professional advice.