To experience drug withdrawal the user must have first developed a physical/psychological dependence to the drug.
PCP users often experience several unpleasant psychological effects, with symptoms mimicking schizophrenia (delusions, hallucinations, disordered thinking and extreme anxiety).
Some herbal remedies can have harmful effects when mixed with alcohol.
The use of amphetamines is currently one of the biggest drug threats in the nation, especially the supercharged version called crystal meth.