Which of the following is NOT a common effect of stimulants?

The assertion that weight gain and lethargy is not a common effect of stimulants is accurate. Stimulants, by their nature, are substances that increase alertness, attention, and energy, often leading to weight loss rather than weight gain. They are known to enhance certain neurotransmitters in the brain such as dopamine and norepinephrine, which typically result in increased energy and heightened alertness. This often translates into feelings of euphoria and enhanced physical activity, contrasting sharply with the idea of lethargy.

Common effects of stimulants include heightened alertness and a feeling of well-being, which can lead to anxiety in some users as well. In severe cases, excessive use of stimulants can even lead to dangerous conditions, including anxiety or, in extreme cases, failure in bodily systems, which can be life-threatening. Thus, associating stimulants with weight gain and lethargy does not align with their physiological effects or user experiences typically observed.