Which criterion is essential in assessing whether a person has developed tolerance to a substance?

The essential criterion in assessing whether a person has developed tolerance to a substance is the increased amount needed to achieve the desired effect. Tolerance occurs when the body becomes accustomed to the presence of a substance, leading to a reduced response to its effects over time. As a result, individuals often find that they need to consume larger quantities of the substance to achieve the same effect that they initially experienced with a smaller amount. This phenomenon is a hallmark of substance use disorders and signifies physiological changes in the body's response mechanisms.

While decreased appetite, uncontrolled cravings, and physical symptoms upon withdrawal are significant aspects of substance use disorders, they do not directly indicate the development of tolerance. Decreased appetite may relate more to the substance's effects or withdrawal, cravings indicate a desire for the substance that may or may not be related to tolerance, and withdrawal symptoms are indicative of physiological dependence rather than tolerance specifically. Therefore, the increased amount needed to achieve desired effects serves as the primary measure for assessing tolerance development.