PCP is not technically a horse tranquilizer, though that nickname has stuck for decades. It was originally developed as a human anesthetic in the 1950s and later used on some animals, but horses were never its primary target. The “horse tranquilizer” label is more street slang than scientific fact, and it often gets mixed up with ketamine, a related drug that actually is used in veterinary medicine today.
What PCP Was Actually Made For
PCP, short for phencyclidine, was first discovered in 1926 and developed as a general anesthetic for humans during the 1950s. It was marketed under the brand name Sernyl and began being used in surgical procedures in 1963. Doctors valued it because it could produce pain relief and unconsciousness without dangerously suppressing heart rate or breathing, a significant advantage over other anesthetics available at the time.
That changed quickly. Patients waking up from PCP anesthesia frequently experienced psychosis, extreme agitation, delirium, violent behavior, and hallucinations. These post-operative reactions were severe enough that PCP was pulled from human medical use.
The Veterinary Connection
After PCP failed as a human anesthetic, it was repackaged under the brand name Sernylan for veterinary use. But even in animal medicine, it wasn’t primarily used on horses. Sernylan was used on dogs, nonhuman primates, and was actually the preferred anesthetic for crocodilians. Its last commercial use in the United States was in 1978, after which it was discontinued entirely.
So where did “horse tranquilizer” come from? The nickname appears to be street slang that loosely references PCP’s veterinary history without much accuracy. Other street names follow the same pattern: “hog” and “elephant” both nod to the idea that PCP is strong enough to knock out large animals. None of these names reflect how the drug was actually used in veterinary practice.
How PCP Differs From Ketamine
The confusion deepens because ketamine, a chemically related drug, genuinely is used as an animal tranquilizer, including on horses. Both PCP and ketamine are dissociative anesthetics that work by blocking a specific type of receptor in the brain involved in learning, memory, and pain signaling. Ketamine was developed partly as a safer alternative to PCP, and it remains in use today for both human and veterinary medicine. When people call PCP a “horse tranquilizer,” they’re sometimes conflating it with ketamine’s actual veterinary role.
What PCP Actually Does
PCP works by blocking communication at certain receptors in the brain, creating a dissociative state where a person feels detached from their body and surroundings. At lower doses, this can produce numbness, a floating sensation, and distorted perception. At higher doses, the effects become far more dangerous.
The drug can be snorted, injected, smoked, or swallowed. One common method involves dipping cigarettes or marijuana joints in liquid PCP, sometimes called “wet” or “sherm” on the street. Other street names include angel dust, embalming fluid, love boat, peace pill, rocket fuel, and wack.
What made PCP problematic as a medical anesthetic is exactly what makes it dangerous as a street drug. It can trigger intense psychosis, paranoia, and agitation, sometimes lasting hours. Users may become extremely combative or appear to feel no pain, which contributes to PCP’s reputation for making people seem almost superhumanly difficult to restrain. These effects are unpredictable and can vary widely from one use to the next.
PCP’s Legal Status Today
PCP is classified as a Schedule II controlled substance by the DEA, meaning it has a high potential for abuse that can lead to severe psychological or physical dependence. Despite that classification (which technically allows for limited medical use), PCP is no longer produced or used for any medical purpose in the United States. Its manufacture is outlawed, and all PCP found on the street is produced illegally.
The drug’s entire medical lifespan was remarkably short. It went from promising surgical anesthetic in 1963 to completely abandoned by 1978, a span of just 15 years. What remains is its reputation on the street and a nickname that never quite matched the reality of how it was used.