People who use PCP can get physically or psychologically (mentally) addicted to the drug. If an addicted person suddenly stops taking PCP, he will get withdrawal symptoms, like diarrhea, chills, and tremors (uncontrollable shaking in part of the body). In the brain, PCP affects multiple neurotransmitter systems. (Neurotransmitters are chemical messengers in the brain.) For example, it keeps the brain from getting rid of extra dopamine, norepinephrine, and serotonin. These are all very important neurotransmitters in the brain. PCP can also affect some types of opioid receptors in the brain. It also inhibits (or blocks) the action of glutamate by blocking NMDA (N-methyl d-aspartate) receptors. Prescription drugs like diazepam (Valium), haloperidol (Haldol), and phentolamine may be used to help manage some of PCP's effects.