Many different drugs produce different withdrawal symptoms. Withdrawal symptoms occur when a drug, which a person has developed a tolerance to, and cannot function normaly without, is taken away. Withdrawal symptoms can be both physical and psychological. These symptoms are usually the exact opposite of the effects produced by the drug.

Some examples:

Caffeine
Someone who is addicted to caffeine may suffer from nervousness, instability, headaches, drowsiness, and decreased alertness, and increases in blood pressure.

Amphetamines
A person withdrawing from amphetamines is physically exhausted, sleeping many hours at a time, in a stupor, and extremely depressed and intensely hungry when they are awake.

Narcotics
After only 6-24 hours of abstaining the addict experiences nausea, diarrhea, depression, stomach cramps, insomnia, and pain that grows worse and worse until they are intolerable

Tranquilizers
A person withdrawing from tranquillizers become nervous and agitated.