Marijuana, including medical marijuana; phencyclidine, called angel dust or PCP; and lysergic acid diethylamide, or LSD, are drugs that can cause paranoia, according to MedlinePlus. Derived from cannabis or hemp plants, marijuana can create feelings of paranoia, excessive fearfulness and delusions in its users, even in low amounts. People who take PCP in large doses may experience paranoia, auditory hallucinations, and other schizophrenia-like symptoms. Minute amounts of LSD can cause paranoia because it is a strong hallucinogen.
Marijuana is a drug that affects the central nervous system, notes MedlinePlus. The primary ingredient in marijuana is delta-9-tetrahydrocannabinol, or THC, which is in the flowers and leaves of the hemp plant. THC is the main ingredient of medical marijuana, which is legal in more than 15 states as of 2015.
PCP, a powdery white substance that dissolves in water or alcohol, is an illegal drug, states MedlinePlus. PCP users take it orally, smoke it and inject it intravenously. The time it takes for the drug to have an effect depends on the method of ingestion. Intravenous injections and smoking the drug result in the fastest reaction times, with users feeling effects within five minutes.
LSD users can experience extreme anxiety, see things that are not there and suffer other delusions, explains MedlinePlus. Drug users refer to the symptoms as bad trips, and they can recur even after cessation of regular use.