What is a common effect of stimulants on the central nervous system?

Stimulants are known to increase activity in the central nervous system, leading to heightened levels of alertness, energy, and focus. This effect is due to the way stimulants, such as caffeine, amphetamines, and cocaine, work by increasing the release of certain neurotransmitters like dopamine and norepinephrine. As a result, individuals often experience improved concentration, faster processing of information, and an overall feeling of being more awake and energized.

In contrast, the other options pertain to effects that are characteristic of depressants or sedatives, which tend to lower central nervous system activity. Therefore, the impact of stimulants on enhancing focus and alertness clearly distinguishes them from other classes of substances, making this a defining characteristic of stimulant use.