Semax.

Raising growth factors that support neuronal survival, synapse formation, and plasticity.

Neurotrophic factors are proteins that keep neurons alive, guide the formation and strengthening of synapses, and support the structural changes underlying learning. The best-studied is brain-derived neurotrophic factor, which acts on the TrkB receptor tyrosine kinase to activate PI3K and Akt signalling for survival and MAPK signalling for growth, and which is required for long-term potentiation, the cellular process most closely associated with memory formation. Nerve growth factor acts similarly through TrkA. A separate system involves hepatocyte growth factor and its receptor tyrosine kinase c-Met, which in neurons is associated with dendritic spine formation and synaptogenesis. Compounds in this group approach the same idea from different angles. Several are short peptides derived from fragments of adrenocorticotropic hormone that lack the hormone's melanocortin-driven corticotropic activity, so they do not raise cortisol. Their best-characterised action in animal and cell studies is upregulation of BDNF and its TrkB receptor in the hippocampus and cortex, along with increased nerve growth factor expression, plus modulation of monoaminergic signalling and inhibition of enkephalin-degrading enzymes. One member of this subgroup is a chemically modified variant designed for greater stability, whose mechanism is inferred from the parent rather than independently established. Others are complex biological mixtures rather than single molecules, prepared from brain tissue, and their activity is attributed to many peptide interactions acting together. Proposed actions include mimicking endogenous neurotrophic factors, supporting neuronal energy metabolism, reducing excitotoxicity, and providing anti-apoptotic and antioxidant effects. Because the active components are not fully defined, batch consistency is an intrinsic issue with this format. A further compound is reported to raise BDNF transcription while inhibiting a cytokine signalling pathway, with downstream reduction of an enzyme implicated in abnormal tau phosphorylation. Another was developed to potentiate hepatocyte growth factor signalling at c-Met. Several honest caveats apply. Most of this evidence comes from rodent and cell-culture work. Some of the brain-derived mixtures are approved and widely used in certain countries while remaining unapproved and unavailable in others, and independent assessments of their clinical benefit have been mixed. For the c-Met compound, the central biochemical evidence for its proposed mechanism came from a publication that was retracted for data fabrication, and c-Met is a well-established oncology target, so chronic potentiation raises an unresolved risk question that no human study has addressed.

Peptides that tune monoamine, GABA, opioid, ion-channel, and social-behaviour circuits.

Neuromodulation differs from neurotransmission. A neurotransmitter carries a discrete signal across a synapse; a neuromodulator adjusts how strongly and for how long many synapses respond, acting over a broader area and a longer timescale. Most of the compounds grouped here are neuromodulators, which is why their reported effects are described as shifts in tone rather than as switching a function on or off, and why their effects are often bidirectional depending on the starting state. Several routes are represented. One compound is a selective blocker of TREK-1, a two-pore-domain potassium channel. These channels set the resting membrane potential and therefore how easily a neuron fires. TREK-1 is expressed in mood-relevant regions and has been implicated in resistance to conventional antidepressants, and blocking it is proposed to increase serotonergic neurotransmission and support hippocampal neurogenesis. This is a well-defined molecular target, which distinguishes it from most of the group. Another is derived from an immune-active parent peptide and retains immunomodulatory activity while shifting toward central effects. Its proposed actions include modulation of serotonin, dopamine, and noradrenaline systems, interaction with GABAergic signalling, and inhibition of enkephalin-degrading enzymes, which prolongs the action of the body's own opioid peptides rather than adding an exogenous one. A third acts on the oxytocin receptor, a G-protein-coupled receptor. Peripherally this drives uterine contraction and the milk ejection reflex, which is the basis of its approved obstetric use. Centrally, oxytocin signalling in the amygdala, nucleus accumbens, and hypothalamus is associated with social salience, threat processing, and reward related to social interaction. Effects here are strongly context-dependent and are not reliably prosocial. A fourth has no confirmed receptor at all despite decades of study. Reported interactions are diffuse and concentration-dependent, spanning NMDA receptor modulation, stress-axis regulation, and several neuropeptide systems, and it has been framed as a homeostatic regulator with dose- and timing-dependent effects rather than as a sedative acting at a defined site. Honest assessment: one member is an approved medicine for a narrow peripheral indication, and its central effects remain an active research question rather than an established therapy. The others are unapproved research compounds whose mechanisms rest largely on rodent and in vitro work, with limited independent human evidence. Compounds affecting mood and arousal circuits also interact unpredictably with psychiatric medication.

It is an approved drug in Russia and appears on its list of vital and essential medicines, but national approval is not the same as independently replicated efficacy evidence.

A controlled Russian study in ischemic stroke reported better motor recovery and functional independence alongside rehabilitation, but no large independent double-blind Western trial has replicated the finding.

BDNF and TrkB upregulation is documented in rat and in vitro work; human data are limited and a circulating marker change is not the same as demonstrated brain neurotrophic action.

Cognitive-enhancement and ADHD uses rest largely on hypothesis papers rather than rigorous trials, and subjective cognitive outcomes are among the most placebo-responsive endpoints in medicine.

The tolerability record covers an approved intranasal pharmaceutical in one country, not research-grade material of unverified purity used by other routes or in unstudied populations.