What is a common warning sign of drug addiction?

The correct choice highlights that having no money can often be a common warning sign of drug addiction. Individuals struggling with substance abuse may prioritize spending on drugs over other financial responsibilities, leading to financial instability. This pattern often manifests in a lack of funds for necessities, as well as decreased ability to meet obligations such as bills or groceries.

In contrast, increased social activity, heightened productivity, and consistent happiness are typically not aligned with behaviors seen in addiction. While someone may temporarily experience these states, they are not indicative of drug addiction. In fact, increased social isolation and a decline in productivity and overall happiness are more closely associated with the detrimental effects of substance use.