Alkaloid/ˈælkəlɔɪd/ Definition 1 of 1Pro Tip 1/3Plant Origin Alkaloids come from plants and often have strong effects on humans and animals. The alkaloid in belladonna can cause dangerous symptoms if ingested. Pro Tip 2/3Medicinal Use Some alkaloids, like morphine, are used in medicine for their potent effects. The pain-reliever morphine is an alkaloid extracted from opium poppies. Pro Tip 3/3Diverse Effects Alkaloids can be stimulants, sedatives, or poisons, affecting various bodily functions. Caffeine is a stimulating alkaloid found in coffee and tea.