Scarecrow is a villain from the DC Comics universe who often fights Batman and his allies. Scarecrow had a PHD in psychology and was an expert in the study of fear before he decided to use his talents to commit crimes. His primary weapon is a fear toxin he created himself, which causes its target to experience vivid hallucinations of whatever they fear the most. These hallucinations cause the victim to become terrified and confused, leaving them unable to stop Scarecrow from accomplishing his goals. This fear toxin is a potent weapon, and Scarecrow has used it as a gas and an injected liquid throughout his villainous career.
Although I have not found any evidence that work is being conducted on creating a real world equivalent of Scarecrow’s fear toxin, such a thing is possible. However, doing so would most likely go against the current international treaties that forbid the use of chemical weapons, and so it is unlikely to be an area of research. If a group decided to develop such a weapon, it would have some difficulties in doing so. There are already drugs that create hallucinations and can cause feelings of fear or terror in their users, including “bath salts,” LSD, and various amphetamines, and it might be possible to use these drugs as the basis for something similar to Scarecrow’s fictional concoction. There are problems with attempting this, however, as the effect of these drugs is never guaranteed and can create vastly different effects from person to person. While the drug may cause terror in one person, it can cause euphoria in another, making it unpredictable and potentially useless. Another problem is that drugs such as these carry a severe risk of overdose, and so the amount of drug the target is exposed to would have to be carefully controlled. This would be especially difficult since some people are naturally more or less affected by the drug, and so would need a smaller or larger dose. In order to create a useful version of Scarecrow’s weapon, researchers would most likely have to discover and extract the specific chemicals within these drugs that cause hallucinations and fear, separating them from the parts that cause other reactions. Even this is not guaranteed, however, as the reactions chemicals create in the brain are complex and varied. In order to make this chemical useful as a non-lethal weapon, the dangerous side-effects would also have to be eliminated, a tricky proposition when working with something that directly modifies brain chemistry.
Even if researchers are able to overcome the hurdles that would be involved in creating a toxin that causes fear and hallucinations with no risk of side-effects or permanent damage, they would still need to devise an effective delivery system. In order to be useful, the toxin would need to be delivered at range, and so it would either have to be injected through darts or made into an aerosol or gas. Modern dart guns would be unsuitable for use in combat, as they are single-shot weapons with a long reload time, a short effective range, and an inability to penetrate body armour. Because of these limitations, it is likely that any attempt to weaponize a fear toxin would require it to be in aerosol or gaseous form. These delivery methods allow for long-range delivery, as canisters containing the agent can be dropped or fired into the target area, and the clouds produced can affect more than one person. It is this factor that is also a major problem with any type of gas-warfare, as was discovered during World War I. Gas or aerosol clouds are very vulnerable to winds, which can break up the clouds or move them to another area, and reported cases occurred during World War I of gas attacks drifting back into friendly lines. Gas weapons are also much less dangerous than they once were, due to improvements in defensive measures like gas masks, NBC (Nuclear, Biological, Chemical) gear, and environmental sealing of vehicles.
With all these problems it is doubtful that a fear toxin like that used by Scarecrow will ever be produced, which may be for the best. It seems that Scarecrow’s main weapon, like a great number of other devices that appear in science fiction, works well in the stories where it is featured but is far too impractical for use in the real world.