Plant alkaloids are naturally occurring compounds found in various plants. They often have a bitter taste and can affect the human body in different ways, including acting as stimulants, sedatives, or pain relievers. Common examples include caffeine from coffee, morphine from opium poppies, and nicotine from tobacco. These compounds play a crucial role in plant defense, helping to deter herbivores and protect against pathogens. Due to their biological activity, many plant alkaloids are used in medicine and pharmacology, contributing to the development of various drugs and treatments for numerous health conditions.