Final answer:
Physical cravings and withdrawal symptoms are indicative of physical dependence on a drug, which is separate from psychological dependence and involves a physical need for the substance to avoid withdrawal. Tolerance often accompanies physical dependence, and methadone may be used to help manage heroin addiction by reducing withdrawal symptoms.
Step-by-step explanation:
Physical cravings for a drug and unpleasant reactions when the drug is withheld are signs of physical dependence. This condition, wherein stopping the use of a substance causes physical and/or psychological symptoms, is distinct from psychological dependence, which refers to an emotional, rather than physical, need for the drug. Individuals experiencing physical dependence may also show signs of tolerance, needing increased amounts of the substance to feel the same effects, and may suffer from withdrawal symptoms when not using the drug.
Why might a person with a heroin addiction be prescribed methadone? Methadone is a psychoactive drug used in the treatment of heroin addiction to reduce withdrawal symptoms and to help manage the addiction, contributing to the process of rehabilitation and recovery.