What this is about
Many naturally occurring and synthetic chemicals that affect the central nervous system (CNS) can cross from the bloodstream into the brain, influencing human behavior and bodily functions, sometimes beneficially, sometimes harmfully. As brain weapons, for instance.
Why you should read this
When these substances alter brain activity, they can change how people think, feel, and act. That makes them powerful tools for medicine—but also potential weapons.
What are CNS-active substances?
CNS (central nervous system)-active compounds influence how the brain and spinal cord function. Doctors use them to relieve pain or treat mental health disorders. But the same knowledge can also be applied to paralyze, disorient, or incapacitate people, which makes these substances inherently risky.
In food and medicine
Natural products such as plant extracts and herbal supplements are increasingly used worldwide for their potential therapeutic effects on the nervous system. For example, açaí berries may slow the progression of Parkinson’s disease, while ashwagandha—a plant from Ayurvedic medicine—appears to promote the regeneration of nerve cells damaged by Alzheimer-like processes.
Yet new research shows these substances can also carry serious risks. Scientists tested hundreds of natural compounds to see whether they could cross the blood–brain barrier, the body’s natural filter that protects the brain from harmful chemicals. About 40 percent (255 compounds) did so successfully—an important finding for their medical potential, but also a red flag for possible toxicity.
Many of these compounds, also found in foods, cosmetics, and hormonal disruptors, may have underestimated effects on the central nervous system and should be studied far more systematically. Further testing revealed that roughly 35 percent of the substances inhibited the growth of nerve fibers—an indicator of potential neurotoxicity.
CNS-active chemicals as weapons
Two British researchers, Michael Crowley and Malcolm Dando from the University of Bradford, warn in a new book that advances in neuroscience, pharmacology, and artificial intelligence could pave the way for so-called “brain weapons”: CNS-active agents capable of manipulating consciousness, memory, or behavior.
These could include incapacitating agents, designed to temporarily disable people without permanent harm, such as certain opioids (for instance, fentanyl). Other CNS-acting chemicals function as chemical weapons, capable of causing severe injury or death by disrupting nerve function.
No longer science fiction
The researchers argue this is no longer the stuff of science fiction. They point to the notorious Moscow theater siege of 2002, when Russian forces used fentanyl derivatives to end a hostage crisis, killing more than 120 hostages. Since then, technology has advanced dramatically, heightening the risk of misuse by state actors.
The use of such chemicals is strictly prohibited under the Chemical Weapons Convention (CWC). Nations are banned from developing or stockpiling them for military purposes. Even use by law enforcement poses major ethical risks. Those risks increase further when governments ignore international treaties or ethical boundaries.
Their warning highlights an urgent ethical and security dilemma: the line between medical innovation and military exploitation of brain science is rapidly blurring, while international oversight weakens and compliance erodes.
