Semax

Semax is a synthetic heptapeptide with the sequence Met-Glu-His-Phe-Pro-Gly-Pro (MEHFPGP). It is a structural analogue and fragment of adrenocorticotropic hormone (ACTH), specifically derived from the ACTH(4-10) sequence with stabilizing Pro-Gly-Pro additions that extend its bioactivity and resistance to enzymatic degradation. Crucially, while Semax retains the neurotrophic properties of the ACTH fragment, it lacks the hormonal activity of full-length ACTH and does not stimulate cortisol release from the adrenal glands. This separation of neurotrophic from hormonal effects makes Semax pharmacologically unique. It has been registered as a pharmaceutical in Russia and CIS countries for decades, where it is clinically prescribed for stroke recovery, traumatic brain injury, optic nerve disease, and cognitive decline.

Semax operates through several distinct neurobiological mechanisms that collectively explain its cognitive-enhancing and neuroprotective profile. Most prominently, Semax significantly upregulates brain-derived neurotrophic factor (BDNF) and its receptor TrkB in the hippocampus. A single administration of Semax at 50 mcg/kg produced a 1.4-fold increase in BDNF protein and a 3-fold increase in BDNF mRNA expression in published rodent studies. BDNF is the primary driver of synaptic plasticity and long-term potentiation, making its upregulation central to improved memory formation and learning. Semax also modulates serotonin, dopamine, and acetylcholine neurotransmitter systems, suppresses neuroinflammatory gene expression, and activates expression of genes related to neurotransmission.

In the context of ischemic brain injury, Semax has demonstrated particularly robust effects. Genome-wide transcriptional analysis following middle cerebral artery occlusion (pMCAO) in rats showed that Semax dramatically shifted gene expression away from inflammatory pathways and toward neurotransmission and vascular repair pathways. In a photothrombosis model, six daily administrations of Semax at 250 mcg/kg reduced infarction size and improved performance on cognitive tasks. Semax also has the notable property of interacting with copper ions (Cu2+), potentially interfering with the formation of beta-amyloid-copper complexes implicated in Alzheimer's disease pathology, though this mechanism remains a subject of ongoing investigation.

Clinical use of Semax in Russia has been documented over more than two decades, with applications in stroke rehabilitation, optic nerve atrophy, peptic ulcer disease, and cognitive decline in aging. A pilot study in 24 healthy subjects found that intranasal 1% Semax (total dose 1.2 mg) increased resting fMRI signal in the default mode network compared to placebo, suggesting measurable central nervous system effects at doses relevant to cognitive enhancement use. The compound is not approved by the FDA or EMA, and the published evidence base, while mechanistically compelling, lacks the large-scale randomized controlled trials that would be required for regulatory approval in Western countries.