An alkaloid is a class of naturally occurring organic compounds that mostly contain basic nitrogen atoms. They are found in various plants and can have pronounced effects on humans and animals. Common examples include morphine, caffeine, and nicotine. Alkaloids are often used for their medicinal properties, as some can act as analgesics, stimulants, or sedatives, while others can be toxic. The diverse biological effects exhibited by alkaloids make them significant in pharmaceuticals and herbal medicine.