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Since 2020, millions of people have reported a similar set of symptoms. They describe brain fog, difficulty concentrating, reduced motivation, memory problems, mental fatigue, and a feeling that they are no longer operating at the same mental level they once did. Some noticed these changes following a COVID infection, while others experienced them during years marked by chronic stress, disrupted sleep, isolation, and major lifestyle changes. Regardless of the cause, one question continues to surface: why do so many people feel like their brain changed?
Researchers believe there is no single explanation. Brain health is influenced by sleep, stress, inflammation, physical activity, nutrition, and social connection. What makes the post-pandemic period unique is that many of these factors worsened simultaneously, creating conditions that may affect cognitive performance across large populations.
One of the most studied biological factors involved in learning and memory is Brain-Derived Neurotrophic Factor, or BDNF. Often described as “fertilizer for the brain,” BDNF helps neurons grow, communicate, adapt, and survive. It plays a central role in neuroplasticity, the brain’s ability to form new connections, strengthen existing pathways, and adapt to new experiences. Researchers have observed that chronic stress, poor sleep, depression, and inflammation are all associated with reduced BDNF activity, making it a major area of interest for scientists studying cognitive decline and recovery.
This growing interest in BDNF is one reason researchers began investigating Semax. Developed in Russia during the 1980s, Semax is a synthetic peptide derived from adrenocorticotropic hormone (ACTH) and has been studied for decades in neurological settings. Researchers have explored its potential role in learning, memory, attention, neuroprotection, stroke recovery, and cognitive performance.
One of the most frequently cited studies involved 110 patients recovering from ischemic stroke. Participants received two ten-day treatment courses of Semax at 6,000 micrograms per day. Researchers reported improvements in neurological recovery and functional outcomes while also observing evidence of increased neurotrophic activity and neuronal repair pathways. Additional laboratory research suggested that Semax may influence genes associated with BDNF production, leading scientists to investigate whether the peptide could support learning, memory, adaptation, and recovery following neurological stress.
Semax has attracted additional attention because its potential effects may extend beyond BDNF. Research suggests it may influence dopamine and serotonin signaling, neurotransmitter systems heavily involved in focus, motivation, emotional regulation, and mood. Experimental studies have also demonstrated reductions in inflammatory activity and oxidative stress markers, two processes that have been linked to cognitive decline and neurological dysfunction. Together, these findings have positioned Semax as one of the most researched cognitive peptides currently being discussed within the peptide community.
While Semax is often associated with cognition and neuroplasticity, another Russian-developed peptide has attracted attention for a different reason. Selank is a synthetic peptide derived from tuftsin and has been studied primarily for its potential effects on anxiety, stress resilience, emotional regulation, and overall psychological well-being.
This distinction is important because many people experiencing brain fog and mental fatigue are also dealing with chronic stress, poor sleep, anxiety, and emotional exhaustion. Researchers increasingly recognize that cognitive performance and emotional health are deeply connected. A brain operating under persistent stress is often less capable of maintaining attention, processing information efficiently, and performing at its highest level.
One of the most frequently cited human studies involved 62 patients diagnosed with Generalized Anxiety Disorder and neurasthenia, a condition characterized by fatigue, irritability, weakness, and mental exhaustion. Researchers compared Selank to medazepam, a benzodiazepine commonly prescribed for anxiety. The findings were notable because Selank demonstrated anti-anxiety effects while also showing anti-fatigue and mild psychostimulant properties. Researchers further reported that Selank did not produce the same level of sedation or cognitive impairment commonly associated with traditional benzodiazepines.
Scientists believe part of Selank’s activity may involve the GABAergic system. GABA, or Gamma-Aminobutyric Acid, acts as the brain’s primary inhibitory neurotransmitter and helps regulate stress responses, calm excessive neural activity, and maintain emotional balance. Laboratory studies have also suggested that Selank may influence serotonin pathways, which play a major role in mood, emotional regulation, sleep quality, and psychological well-being. These findings have helped establish Selank as one of the most intriguing peptides being studied for stress-related cognitive and emotional symptoms.
Perhaps the most interesting aspect of Semax and Selank is that they appear to target different sides of the same problem. Semax is primarily studied for learning, memory, neuroplasticity, BDNF activity, and cognitive performance. Selank is more commonly associated with anxiety reduction, emotional regulation, stress resilience, and nervous system balance. Together, they represent two different approaches researchers are exploring in an effort to better understand how the brain learns, adapts, performs, and recovers.
Researchers are still working to understand why so many people continue to report cognitive and emotional challenges years after the pandemic began. What they do know is that these symptoms are widespread, persistent, and deserving of serious investigation. The growing interest in BDNF, Semax, and Selank reflects a broader effort to understand how the brain responds to stress, adapts to change, and recovers from adversity. For many people, the goal is not becoming smarter than they were before. The goal is simply feeling like themselves again.
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