Erik is a 26-year-old patient who abuses heroin. He states to you, "I’ve been using more heroin lately. I told my counselor about it and she said I need more and more heroin to feel the effect I want." Which of the following does this describe?

Choice A reason: Tolerance is a physiological state in which repeated exposure to a substance results in a diminished response, requiring increasingly larger doses of the drug to achieve the same initial effect or desired "high." This occurs due to neuroadaptation at the cellular and receptor levels within the central nervous system. Choice B reason: Intoxication refers to the acute state of being under the influence of a substance, resulting in maladaptive behavioral or psychological changes. While Erik is a user, the statement specifically addresses the need for increased quantity over time rather than the immediate physiological effects of a single dose of heroin. Choice C reason: Withdrawal consists of the specific physical and psychological symptoms that occur when a person stops or reduces the intake of a substance they are dependent upon. Erik is describing the process of increasing his usage to maintain effect, rather than the symptoms of distress following the cessation of the drug. Choice D reason: Addiction, or substance use disorder, is a broad clinical diagnosis encompassing compulsive drug seeking, loss of control, and continued use despite negative consequences. While tolerance is a common physiological component of addiction, Erik's specific description of needing more drug for the same effect is the precise definition of tolerance.