Final answer:
Substance abuse is the inappropriate use of drugs leading to harm, and can escalate into drug addiction and dependence. Tolerance, where more of the drug is needed to feel its effects, and psychological dependence, characterized by drug craving, are important components of addiction.
Step-by-step explanation:
The use of unacceptable drugs and/or the excessive or inappropriate use of acceptable drugs in ways that can lead to physical, psychological, or social harm defines substance abuse. This condition often indicates the presence of a drug addiction, where there is compulsive use of a substance such as a psychoactive drug despite the negative consequences that such use may entail. Over time, this can lead to drug dependence, where the user experiences withdrawal symptoms upon cessation and may develop tolerance, needing more of the drug to achieve the same effects, potentially leading to an overdose.
Tolerance occurs when a drug user requires more and more of a given drug in order to experience the same effects of the drug. It is linked to physiological dependence and can cause the user to increase the amount of drug used to a dangerous level, even to the point of overdose and death. Psychological dependence, or drug craving, is characterized by an emotional need for the drug and may drive an individual to continue using to relieve psychological distress. It's important to understand that psychological dependence can exist even in the absence of physical dependence, as it refers to the craving rather than physical withdrawal symptoms.