Caffeine is a purine alkaloid that has been found in over 60 plant species, which stimulates the central nervous system and causes the consumer to become more awake and alert. Although, continued use can case mild physical dependence to the substance. After cessation of long term use, symptoms of headache, fatigue, concentration difficulties, depressed mood, and irritability may occur for a few days. However, these withdrawal symptoms are considered to be relatively mild in comparison to long term use of alcohol or other drugs (http://www.webmd.com/balance/caffeine-myths-and-facts). The young leaves of these plants exhibit a higher capacity for caffeine biosynthesis than mature leaves (WHAT ARE "THESE PLANTS"? only in caps to draw attention.
