Final answer:
The most severe complication of a PCP overdose is respiratory distress, but cardiovascular collapse, seizures, and psychosis are also critical concerns.
Step-by-step explanation:
The biggest complication of PCP (phencyclidine) overdose is respiratory distress. However, other severe complications can also arise, such as cardiovascular collapse, seizures, and psychosis. Each of these issues poses a significant risk and can be life-threatening. PCP is a potent substance that affects the central nervous system and can lead to a variety of acute and long-term neurological problems if an overdose occurs. Immediate medical attention is critical in managing and treating the complications associated with a PCP overdose.