Which is the best indicator of physical dependence on alcohol or another drug?

Physical dependence on alcohol or another drug is characterized primarily by the body's adaptation to the presence of the substance, leading to the experience of withdrawal symptoms when the substance is reduced or discontinued. These symptoms can manifest in a variety of physical and psychological ways, such as tremors, anxiety, nausea, and in severe cases, seizures. The presence of these withdrawal symptoms serves as a clear indicator that the body has developed a reliance on the substance, reflecting physiological changes that occur with prolonged use.

While the other options—daily consumption, length of use, and frequency of memory blackouts—can provide context and indicate patterns of use, they do not specifically measure the physiological aspect of dependence. For instance, many individuals may consume large amounts of a substance or have years of use without experiencing withdrawal symptoms, indicating that they may not be physically dependent. Therefore, the presence of withdrawal symptoms stands out as the most direct and clinically significant marker of physical dependence.