Which of the following describes caffeine?

Caffeine is classified as an alkaloid, which is a type of naturally occurring organic compound that often has physiological effects on humans and animals. It is commonly found in beverages such as tea and coffee, where it acts as a stimulant by blocking adenosine receptors in the brain, thereby enhancing alertness and reducing fatigue. This characteristic makes caffeine one of the most widely consumed psychoactive substances in the world.

In contrast, the other options present terms that do not accurately define caffeine. While hormones play crucial roles in various biological functions, caffeine does not function as a hormone. It does not stimulate gonadal function nor does it serve as a treatment for heart conditions. Additionally, caffeine is not an anabolic steroid derivative; it is distinct from these substances in its chemical structure and biological effects. Understanding caffeine as an alkaloid helps clarify its role in nutrition and supplementation, particularly how it affects energy levels and overall metabolic processes.