Withdrawal symptoms from heroin begin within 24 hours after last use and may last up to 7-10 days.
The onset of alcohol withdrawal symptoms most often occurs within 5 - 10 hours after the last alcoholic beverage is consumed, but can sometimes begin days later.
PCP users may experience may experience behavioral disturbances and acts of self-injury including suicide, and attacks on others or destruction of property.
Someone who takes antidepressants regularly and is going through withdrawal because of cessation of use will likely experience rebound depression, and may become more depressed than they originally were.