Which of the following is considered a hallmark symptom of substance use disorders?

Loss of control over substance use is indeed regarded as a hallmark symptom of substance use disorders. This symptom reflects a key characteristic of addiction, where individuals find themselves unable to limit or manage their consumption despite a desire to do so. This might manifest as an inability to cut down on substance use, successful attempts to quit being thwarted by cravings or withdrawal symptoms, or continued use despite negative consequences. In essence, loss of control signifies the extent to which the substance use has become a compulsive behavior, overriding an individual's rational decision-making processes and priorities.

In contrast, the other options do not encapsulate the fundamental aspects of substance use disorders. Increased social engagement may be observed in some individuals who utilize substances in social settings but does not directly relate to the disorder itself. Enhanced memory function is generally not associated with substance use disorders, as many substances can impair cognitive function over time, negatively affecting memory. Heightened perception of risk might be true in some contexts, whereby the individual becomes more aware of potential dangers, but it does not specifically identify a symptom of the disorder. Thus, loss of control is the characteristic symptom that defines the struggle those with substance use disorders face.