A drug that helps to decrease appetite is called an _________.

An appetite suppressant is a substance that is specifically designed to reduce hunger or the desire to eat. These drugs are often used in weight management and obesity treatment, as they can help individuals consume fewer calories by diminishing the feeling of hunger. This category of medication works through various mechanisms, including influencing neurotransmitters in the brain that regulate appetite, which can lead to lower food intake and potential weight loss.

The other options refer to different types of medications with distinct purposes unrelated to appetite control. Vasodilators are used to widen blood vessels to improve blood flow, diuretics help remove excess fluid from the body, and antipyretics are used to lower fever. Each of these serves a specific medical function but does not have the effect of suppressing appetite. Therefore, the correct answer identifying the drug that decreases appetite is indeed the appetite suppressant.