Semax half-life: what do studies say about how long it lasts?

What is Semax's half-life?

No half-life for Semax in people was found in the sources read. The FDA's July 2026 briefing document says its staff were not able to find pharmacokinetic studies of Semax in humans (FDA briefing document, July 2026). The closest measured number comes from a test-tube experiment: in the presence of plasma membranes from rat forebrain nuclei, Semax's half-life was longer than 1 hour, a value in rat tissue from an abstract that gives no replicate numbers and does not establish a human result or a human half-life (Dolotov et al., Russian Journal of Bioorganic Chemistry, 2004). The sections below list every other time point found and say what each one measures.

A half-life is the time it takes for the amount of a compound to fall by half. For a peptide that enzymes break down, the figure depends on which fluid or tissue is measured. That is why the 1-hour value cannot be carried over to blood, brain or a person.

In the same test-tube experiment with rat forebrain membranes, the authors consider dipeptidyl-aminopeptidases, enzymes that clip pairs of amino acids off a chain, the main enzymes responsible, and report that they cut Semax in steps to the five-amino-acid fragment His-Phe-Pro-Gly-Pro and then to the tripeptide Pro-Gly-Pro, an in-vitro cleavage result with no replicate count in the abstract that does not establish a human result or human metabolism (Dolotov et al., 2004). A 2006 study in cultures of rat basal forebrain glial and neuronal cells and in plasma membranes reported that splitting off Met-Glu and Gly-Pro and forming pentapeptides were the predominant processes, with different product patterns in glial and neuronal cells; it is a cell-culture result with no replicate count in the abstract that does not establish a human result or human metabolism (Zolotarev et al., Amino Acids, 2006).

Evidence limits

What has not been published about Semax pharmacokinetics?

That is a thinner record than for a compound taken through the usual development steps. The BPC-157 pharmacokinetics page shows what a measured half-life in animals looks like for another research peptide. For Semax, the FDA's briefing says its staff did not identify acute-toxicity or repeat-dose toxicity studies, or additional genotoxicity studies, which normally travel with exposure data (FDA briefing document, July 2026).

How fast does Semax reach the brain in animal studies?

In rats given radiolabelled Semax, radioactivity was already in the brain at the first sample, 2 minutes later: 0.093% of the total radioactivity given was found per gram of brain, and 80% of that was intact Semax, a rat result from an abstract that gives no number of rats and does not establish a human result (Shevchenko et al., Russian Journal of Bioorganic Chemistry, 2006). The FDA's briefing document says 2 minutes was the first time point of blood collection and brain harvesting in that study (FDA briefing document, July 2026), so the study took later samples. This page does not report them, because the abstract does not.

In rats, the 2006 paper reports Semax in the brain within 2 minutes and fast enzymatic breakdown, a rat result from an abstract with no rat count that does not establish a human result or report a half-life (Shevchenko et al., 2006).

What does Semax break down into?

In rats, Semax breaks down into shorter peptide pieces, and the tripeptide Pro-Gly-Pro prevailed in the biological samples relative to Semax and its other metabolites, a rat result with no rat count in the abstract that does not establish a human result (Shevchenko et al., Russian Journal of Bioorganic Chemistry, 2006). In rat blood and serum samples, a bestatin-sensitive aminopeptidase accounted for about one third to one half of the serum degrading activity and clipped the first two amino acids, methionine and glutamic acid, leaving relatively stable intermediates, a test-tube result that does not establish a human result, from an abstract that gives no sample size (Potaman et al., Biochemical and Biophysical Research Communications, 1991).

In rat serum samples, bestatin inhibited up to 66% of the degrading activity, puromycin about 33% and lisinopril about 15%, and the authors concluded that aminopeptidases and angiotensin-converting enzyme account for the major part of the hydrolysis, again a test-tube result with no sample count in the abstract that does not establish a human result (Potaman et al., Peptides, 1993).

In a test-tube assay with rat serum, the 1991 authors report comparable areas under the degradation and accumulation curves for intact peptides and intermediates, and hypothesise that the intermediates can contribute to the effects of the intact peptides, a hypothesis from an abstract with no sample count that does not establish a human result (Potaman et al., 1991).

In rat-serum assays, Semax was more stable than the natural ACTH(4-10) fragment against other serum enzymes, an in-vitro comparison with no sample count in the abstract that does not establish a human result or human persistence (Potaman et al., 1991). The FDA's review says the Pro-Gly-Pro tail is thought to increase stability to peptidases (FDA briefing document, July 2026).

How long do effects of Semax last in studies?

No study read for this page measured how long Semax stays in a person's blood, so duration reports describe effects and not levels. A 1997 review by the Russian group that developed Semax holds the one duration statement among the sources read, and its abstract lists no individual measurements and no participant numbers, so this page does not repeat its figure (Asmarin et al., Zhurnal Vysshei Nervnoi Deiatelnosti, 1997). In a 2018 study of 110 stroke patients, plasma BDNF levels in the Semax subgroups stayed high during the whole study period, which measures the study period and not how long Semax persists, and the abstract gives no subgroup sizes (Gusev et al., Zhurnal Nevrologii i Psikhiatrii, 2018).

The 1997 review is by the compound's developers, and its abstract lists no individual measurements. The 2018 study followed 110 stroke patients through a period that included treatment, so its raised BDNF describes the study period and not the time Semax itself remains in the body (Gusev et al., 2018). The FDA's briefing document says it did not consider Russian-language references that lacked a full English version (FDA briefing document, July 2026).

At what times did studies measure a change after Semax?

No study read for this page defines when Semax takes effect in a person, because each reported time is a measurement point. In rats, radiolabel was in the brain at 2 minutes; the abstract gives no rat count, uptake is not an effect, and this does not establish a human result (Shevchenko et al., 2006). Resting brain scans of 14 healthy adults given Semax and 10 given placebo were taken 5 and 20 minutes after treatment, and the abstract reports a larger volume of one default-mode-network subcomponent in the Semax group without saying at which scan, so it gives no onset (Lebedeva et al., 2018).

In cultured rat glial cells, the greatest rise in neurotrophin messenger RNA came at 30 minutes, with BDNF messenger RNA up eight-fold and NGF five-fold, a cell-culture result on gene activity, with no replicate count in the abstract, that does not establish a human result (Shadrina et al., 2001). In rats, gene changes measured at 1 hour were region-specific, and they measure gene activity and not function, with no rat count in the abstract, and do not establish a human result (Agapova et al., 2007). The table below lists each time point and what it measured.

A time point is when the researchers looked, not when an effect began. A study that scanned at 5 and 20 minutes could not see what happened at 1 minute. What published studies found about Semax sets these results beside the trial record.

What is the half-life of N-acetyl Semax amidate (Na-Semax)?

No half-life for N-acetyl Semax amidate was found. A PubMed search on 14 October 2026 for 'N-acetyl semax', 'N-acetyl-semax' or 'Na-Semax' returned no records. A 2013 paper titled 'Stability of Semax acetyl to proteolysis in various biological media' exists (Shevchenko et al., Doklady Biological Sciences, 2013), but its abstract was not available in PubMed or Crossref, so this page reports no result from it. The title does not show whether 'acetyl' means the acetate salt or an acetylated amino end, so it cannot stand in for a half-life.

What is published is about the amino end of Semax. In test-tube experiments with aminopeptidases, swapping the first amino acid, methionine, for alanine, glycine or threonine made the peptide more stable than Semax, a test-tube result from an abstract with no replicate count that does not establish a human result or a half-life for any N-acetylated form (Shevchenko et al., Russian Journal of Bioorganic Chemistry, 2011). Aminopeptidases attack that end first.

The catalogue lists Semax reference material as laboratory stock. The Semax legal status page covers what the regulator records say about derivative names.