PCP (phencyclidine) was originally developed as a general anesthetic in the 1950s and was used in human surgical procedures starting in 1963 under the brand name Sernyl. It was valued for its ability to provide both pain relief and unconsciousness without suppressing heart function or breathing, which were serious risks with other anesthetics of that era. However, it was pulled from human medicine after patients woke up from surgery experiencing severe psychosis, agitation, and distress. Today, PCP has no approved medical use in humans, though it remains classified as a Schedule II controlled substance in the United States.
Why PCP Was Promising as an Anesthetic
First discovered in 1926, PCP sat on the shelf for decades before researchers in the 1950s recognized its potential. Most anesthetics available at the time carried a significant risk: they could slow the heart rate and suppress breathing, sometimes dangerously so. PCP was different. It could render a patient unconscious and block pain while leaving cardiovascular and respiratory function largely intact. That combination made it extremely attractive for surgery, particularly in patients who might not tolerate the cardiovascular side effects of other drugs.
By 1963, Sernyl was being used in operating rooms. Surgeons appreciated its reliability during procedures, and the drug seemed like a genuine advancement in anesthesia.
Why It Was Pulled From Human Use
The problems showed up after surgery, not during it. As patients emerged from PCP-induced anesthesia, a troubling pattern appeared. Many experienced what clinicians call emergence reactions: intense agitation, hallucinations, paranoia, and a disconnected, distressed mental state. Some patients became violent. The dysphoria (a deep sense of unease and disturbance) was severe enough that the benefits of the drug no longer justified its use.
These weren’t rare events. The reactions were frequent and unpredictable enough that manufacturers recalled PCP from the human medical market. The drug’s mechanism helps explain why. PCP blocks a specific type of receptor in the brain involved in learning, memory, and perception. But it also interferes with the recycling of dopamine, serotonin, and norepinephrine, three chemical messengers that regulate mood, arousal, and reward. That broad disruption of brain chemistry is what produced such intense and varied psychological effects as patients regained consciousness.
Veterinary Use Under a Different Name
After being withdrawn from human medicine, PCP found a second life in veterinary practice under the brand name Sernylan. It was used as an anesthetic in dogs, nonhuman primates, and was actually the preferred anesthetic for crocodilians, animals notoriously difficult to sedate safely. The same properties that made it appealing for humans (stable heart rate and breathing during anesthesia) made it useful in animals whose physiology made other anesthetics risky. This veterinary history is where PCP picked up street names like “horse tranquilizer” and “hog.”
Sernylan was eventually pulled from veterinary use as well, largely because of the drug’s growing diversion to illegal recreational markets.
How Ketamine Replaced PCP
Ketamine, developed in the 1960s, is a close chemical relative of PCP and works through a similar mechanism, blocking the same brain receptor. But it differs in several ways that made it far more practical for medicine. Ketamine is less potent, wears off faster, and causes fewer and less severe emergence reactions. It also produces greater overall sedation, which in a clinical setting is actually preferable because patients are less likely to wake up agitated. At higher doses, PCP can cause convulsions, a problem ketamine avoids. Ketamine also works reliably across many animal species, while PCP’s effects vary depending on the species.
These advantages made ketamine a direct and superior replacement. It remains widely used today in both human and veterinary medicine for anesthesia, pain management, and more recently as a treatment for severe depression.
PCP’s Legal Status Today
The DEA classifies PCP as a Schedule II controlled substance, the same category as morphine, fentanyl, and methamphetamine. Schedule II means the government recognizes a high potential for abuse and the possibility of severe psychological or physical dependence. Technically, the Schedule II classification allows for accepted medical use “with severe restrictions,” but in practice no pharmaceutical company manufactures PCP for any medical purpose, and no doctor prescribes it.
Its primary relevance in modern medicine is as a research tool. Scientists use PCP in animal studies to model psychosis and schizophrenia, because the drug reliably produces symptoms (hallucinations, disordered thinking, social withdrawal) that closely resemble those conditions. This research has helped advance understanding of how disrupted brain signaling contributes to psychiatric illness, but the drug itself is not being developed as a treatment for anything.
Why PCP Still Matters in Pharmacology
PCP’s story illustrates a broader pattern in drug development. A compound can perform brilliantly on one measure (keeping patients alive and pain-free during surgery) while failing catastrophically on another (what happens to their mind afterward). The lessons from PCP directly shaped how newer anesthetics were designed and tested, with much greater attention paid to what patients experience during recovery, not just whether the surgery itself goes smoothly.
Ketamine’s success is a direct result of those lessons. So is the growing interest in other drugs that act on the same brain receptor, including newer compounds being explored for depression, chronic pain, and post-traumatic stress. PCP opened the door to an entire class of medicines, even though it turned out to be the wrong drug to walk through it.