In many instances, a craving for a drug can be enforced by a physical urge - where the body needs the drug to maintain a desired state or avoid an unwanted one. In the case of heroin addiction or alcoholism, a craving for the drug is usually strengthened by a strong desire to avoid withdrawal symptoms.
Hunger for drugs. It is caused by drug-induced changes that occur in the brain with the development of addiction and arises from a need of the brain to maintain a state of homeostasis that includes the presence of the drug.
"Craving" is the seventh episode of the first season of the WB original series, Smallville. The episode was written by Michael Green and was directed by Philip Sgriccia. It originally aired on November 27, 2001.