PCP Effects and Side Effects: Brain, Heart and Behavioral Risks

PCP affects more than perception. Acute phencyclidine toxicity can involve the brain, eyes, cardiovascular system, skeletal muscle, temperature regulation and behavior at the same time. The most recognizable combination is altered mental status with nystagmus, hypertension, impaired coordination and either agitation or unusual sedation, but severe cases can progress to seizures, hyperthermia, rhabdomyolysis, coma, intracranial bleeding and major trauma.

The reason PCP can look so inconsistent from one patient to another is pharmacologic. NMDA receptor blockade contributes to dissociation, analgesia, amnesia and psychosis, while catecholamine effects can produce hypertension, tachycardia and agitation. Additional receptor actions can contribute to lethargy or coma. The same substance can therefore produce features that resemble a stimulant, hallucinogen, sedative and acute psychotic disorder.

PCP Effects by Body System

Neurologic Effects: From Dissociation to Seizures and Coma

Dissociation and altered awareness

PCP can make a person feel detached from the body or surroundings, but the clinical effect is not always experienced as a calm “out-of-body” sensation. Sensory information can become disconnected from normal interpretation, so the person may misjudge distance, danger, other people’s intentions or their own physical condition.

Nystagmus

Nystagmus is involuntary rhythmic eye movement and is one of the classic findings of PCP intoxication. Clinical reviews describe horizontal, vertical and rotary forms, with nystagmus present in a large proportion of toxic presentations. Vertical nystagmus is particularly useful because it is not a routine finding in simple alcohol intoxication.

Nystagmus is supportive, not diagnostic by itself. Other neurologic disorders and drugs can also produce abnormal eye movements, so clinicians combine the finding with mental status, blood pressure, coordination, history and toxicology.

Ataxia and impaired coordination

Ataxia can make a PCP-intoxicated person stagger or walk with a wide, unstable gait. That may resemble severe alcohol intoxication, but PCP can simultaneously cause hypertension, nystagmus and profound psychiatric changes. Impaired coordination sharply increases fall and traffic-injury risk.

Seizures

Seizures are a recognized serious complication of PCP toxicity. They matter not only as a neurologic event but because sustained muscle contraction can drive body temperature higher, increase oxygen consumption and contribute to rhabdomyolysis. A seizure can also result in aspiration or traumatic injury.

In emergency evaluation, clinicians consider glucose, electrolytes, co-ingestants, trauma and other causes because PCP exposure does not exclude a second diagnosis. The treatment priority is the patient, not simply proving which drug triggered the event.

Stupor and coma

At the opposite behavioral extreme, PCP can cause profound CNS depression. A comatose patient is at risk for loss of airway protection, aspiration and occult trauma. Reduced consciousness also makes it critical to consider opioids or other sedatives that may have been used at the same time.

Psychiatric Effects: Paranoia, Hallucinations and Disorganization

PCP can cause severe paranoia, hallucinations, delusions, hostility, religious or grandiose ideas and disorganized thinking. Historical clinical series documented distinct patterns including toxic psychosis, catatonic states, acute brain syndrome and coma. The psychiatric presentation can be severe enough to resemble schizophrenia.

The important distinction from a simple frightening intoxication is impaired reality testing. A person with PCP psychosis may be convinced that others intend harm, may respond to voices that are not present or may behave according to a fixed delusional belief. These symptoms can persist beyond the most obvious intoxication in some patients.

See PCP Psychosis for a deeper explanation of diagnosis and duration.

Cardiovascular Effects: Why High Blood Pressure Matters

PCP’s sympathomimetic effects can produce hypertension and tachycardia. StatPearls reports hypertension in about 60 percent of described toxicity cases and tachycardia in about 30 percent, though these figures come from older clinical datasets and should not be treated as modern population prevalence.

The mechanism includes norepinephrine and dopamine effects, agitation and muscular activity. Severe hypertension can contribute to headache, chest symptoms and rare but serious cardiovascular or cerebrovascular complications. Reported complications include myocardial infarction, intraparenchymal hemorrhage and subarachnoid hemorrhage.

Because these complications overlap with cocaine, methamphetamine and other stimulant toxicity, a broad substance history matters. A PCP-positive urine test should not make clinicians ignore a possible stimulant co-exposure.

Hyperthermia, Muscle Rigidity and Rhabdomyolysis

Why body temperature rises

PCP-related hyperthermia is often driven by intense muscle activity rather than a simple thermostat effect. Severe agitation, rigidity and seizures generate heat. If the person is struggling continuously, physically restrained for a prolonged period or in a hot environment, heat production can outpace normal cooling.

How rhabdomyolysis develops

Rhabdomyolysis is destruction of skeletal muscle with release of intracellular material into the circulation. PCP can contribute through several pathways at once: seizure activity, sustained rigidity, extreme agitation, hyperthermia and trauma. The shared mechanism is muscle energy failure and membrane injury.

Released muscle contents include creatine kinase, potassium, phosphate and myoglobin. Hyperkalemia can disturb cardiac rhythm, while myoglobin and dehydration can contribute to acute kidney injury. Rhabdomyolysis can continue to evolve after the person becomes calmer, so clinical improvement in behavior does not automatically mean the medical risk has ended.

What clinicians evaluate

Significant PCP toxicity may prompt testing of creatine kinase, potassium, blood urea nitrogen, creatinine and urinalysis. The PCP clinical review notes that creatine kinase is more reliable for screening than urinary myoglobin because myoglobin can clear quickly. Elevated CK by itself must still be interpreted in context, but it can identify muscle injury before renal complications become obvious.

A large historical series reported rhabdomyolysis in 22 of 1,000 PCP intoxication cases, with several patients requiring dialysis for renal failure. The percentage is not a universal modern risk estimate, but it illustrates that the complication is clinically real rather than theoretical.

Trauma: One of the Most Important PCP Complications

PCP-related injury is caused by a combination of impaired coordination, altered judgment, psychosis and analgesia. The person may walk into traffic, fall from height, collide with objects or sustain injuries during severe agitation. Because pain perception is reduced, major injuries can be missed by both the patient and bystanders.

A classic clinical series reported injuries in 16 percent of cases. More recent reviews continue to emphasize a thorough trauma examination. Head injury is particularly important because confusion or coma can be mistakenly attributed entirely to PCP when intracranial trauma is also present.

This is also why restraint requires care. Prolonged physical struggle can increase muscular activity and worsen hyperthermia or rhabdomyolysis. Modern emergency management favors de-escalation and appropriate chemical sedation when necessary rather than prolonged forceful restraint.

Other Clinically Important Effects and Differential Diagnosis

Respiratory and airway effects

Severe respiratory depression is less common than the neurologic and behavioral features of PCP toxicity, but it can occur. Clinical reviews describe irregular respiration, apnea and airway problems in severely intoxicated patients. Increased oral or airway secretions can add difficulty when consciousness is reduced.

An unresponsive person with slow breathing should be treated as a possible mixed overdose until proven otherwise. PCP itself is not reversed by naloxone, but fentanyl or another opioid may be present and would respond to naloxone.

Hypoglycemia and why glucose is checked

Low blood glucose has been reported in PCP toxicity, and StatPearls recommends bedside glucose testing in altered patients. This is clinically important because hypoglycemia can itself cause confusion, seizure, unusual behavior or coma.

Finding PCP exposure should never stop the search for immediately reversible causes of altered mental status.

Longer-term cognitive and mood effects

Repeated PCP use has been associated with memory problems, impaired thinking, speech difficulties, depression and anxiety. These problems are harder to quantify than acute toxicity because much of the literature is older and chronic users often have polysubstance exposure.

Still, persistent cognitive or psychiatric symptoms deserve assessment. A person should not be told that memory loss, depression or psychosis is automatically permanent, but neither should symptoms be dismissed because the urine test is expected to clear eventually.

How PCP differs from simple alcohol intoxication

Both can cause poor coordination, slurred speech and impaired judgment, but vertical nystagmus, severe hypertension, dissociation, marked analgesia and intense psychosis are more suggestive of PCP. Mixed alcohol-PCP use can blur the picture and deepen impairment.

When the effects become an emergency

Emergency care is needed for seizure, collapse, severe agitation, very high temperature, chest pain, focal neurologic symptoms, major injury, coma, abnormal breathing or psychosis that makes the person unsafe. A severely intoxicated patient can deteriorate even if they have previously used PCP without a medical emergency.

Frequently Asked Questions About PCP Effects

Why does PCP cause nystagmus?

PCP disrupts central neurologic control of eye movements. Horizontal, vertical and rotary nystagmus are well-described signs of intoxication.

Why can PCP cause kidney failure?

Severe muscle breakdown can release myoglobin and electrolytes, which can contribute to acute kidney injury, especially with dehydration or hyperthermia.

Can PCP cause a stroke?

Severe hypertension and intracranial hemorrhage have been reported as complications of PCP toxicity, although they are much less common than altered mental status or agitation.

Can someone be badly injured without feeling pain?

Yes. PCP’s analgesic and dissociative effects can blunt pain perception, which is why trauma may be underestimated.

Can PCP effects last after the person looks sober?

Yes. Cognitive, mood or psychotic symptoms can persist after obvious intoxication has improved.

Sources

• NCBI Bookshelf, Phencyclidine Toxicity: clinical presentation, pathophysiology, laboratory evaluation, complications, disposition and emergency management.
• Phencyclidine Intoxication and Adverse Effects: A Clinical and Pharmacological Review: detailed review of intoxication patterns, rhabdomyolysis, psychosis, testing and management.
• MedlinePlus: Substance Use – Phencyclidine (PCP): consumer medical overview of PCP effects, dependence, withdrawal and treatment.
• Acute phencyclidine intoxication: clinical patterns, complications, and treatment: large clinical series describing intoxication syndromes, injuries and medical complications.
• Phencyclidine abuse, dependence, intoxication, and psychosis: review of PCP-related abuse, dependence and psychiatric effects.

Additional Source

• AAST Critical Care Committee Clinical Consensus on Rhabdomyolysis: pathophysiology of skeletal-muscle breakdown, electrolyte release and acute kidney injury.