Which of the following is a common effect of stimulants?

Increased alertness is a common effect of stimulants because these substances work by enhancing the activity of certain neurotransmitters in the brain, particularly dopamine and norepinephrine. This heightened activity leads to increased focus, attention, and overall cognitive vigilance. Stimulants are often used to combat fatigue and improve performance during tasks that require sustained attention, making individuals feel more awake and capable of processing information more efficiently.

The other options, such as relaxation, drowsiness, and weight gain, are typically associated with depressants or substances that may have sedative effects rather than stimulatory effects. Relaxation is more indicative of calming agents, drowsiness suggests a decrease in alertness and energy, and weight gain is not a direct result of stimulant use, as stimulants are more likely to suppress appetite rather than encourage weight gain.