Caffeine is a considered a safe ingredient. It is a stimulant that excites the nerves cells of the brain. While some stimulants, such as nicotine, are considered addictive, you aren’t likely to become addicted to caffeine if you consume it in moderation. However, habitual consumption can lead to adverse reactions in some people if they don’t get that morning cup of coffee. Those symptoms can include headache, fatigue, difficulty concentrating, nausea, and muscle pain. (http://www.webmd.com/diet/rm-quiz-caffeine-myths?ecd=soc_tw)