Dhruv has been consuming alcohol for many years. Recently he has joined an alcohol rehabilitation center. During his group therapy session, Dhruv shared the amount of alcohol he could drink to feel ’high’. He started with a peg and to get the same effect now he has to take a greater amount. Identify the reason for this change:

The correct option is Tolerance.

Step-by-step Explanation:
1. Understanding the Scenario: The question describes a situation where an individual (Dhruv) needs to consume a larger quantity of alcohol over time to experience the same level of intoxication ("high") that he initially achieved with a smaller amount (one peg).
2. Defining Tolerance: Tolerance is a physiological state that occurs when the body adapts to the repeated presence of a substance, such as alcohol. Because of this adaptation, the effectiveness of a constant dose of the substance decreases with continued use, requiring the user to increase the dosage to achieve the desired effect.
3. Mechanism: With prolonged alcohol consumption, the brain adjusts its neurotransmitter systems to counter the depressive effects of alcohol and maintain normal functioning (homeostasis). Consequently, the brain becomes less sensitive to the same quantity of alcohol, forcing the individual to drink more to feel the same effects.
4. Why other options are incorrect:
- Withdrawal: This refers to the unpleasant physical and psychological symptoms that occur when a dependent person suddenly stops or reduces substance use. It is not the need for increased dosage.
- Poor quality of alcohol: While low-quality alcohol might affect the experience, the progressive need for greater quantities is a biological adaptation in the body, not a result of changes in the product's quality.
- Fixation: In psychology, fixation refers to an obsessive attachment to a person, object, or developmental stage, which is unrelated to this physiological response to a substance.