What type of substance raises levels of physiological or nervous activity in the body?

Stimulants are substances that have the primary effect of increasing physiological or nervous activity in the body. They can enhance alertness, energy, and attention by boosting the activity of certain neurotransmitters in the brain. This increase in activity can lead to heightened feelings of euphoria, improved concentration, and even more rapid heart rates.

In contrast, other substances listed serve different purposes. Narcotics typically provide pain relief and can induce feelings of relaxation or sedation. Depressants slow down brain function and can lead to drowsiness or calming effects. Hallucinogens alter perception, mood, and thought processes but do not primarily increase physiological activity. Understanding these distinctions is crucial in health and safety contexts, particularly in recognizing the effects and potential risks associated with various drug classes.