There is a long standing debate among Mormons as to whether caffeine is permissible or not according the health code Mormons follow, known as the Word of Wisdom. The following quote is one of the few statements from leaders of the Church on the subject of caffeine:
With reference to cola drinks, the Mormon Church has never officially taken a position on this matter, but the leaders of the Church have advised, and we do now specifically advise, against the use of any drink containing harmful habit-forming drugs under circumstances that would result in acquiring the habit. Any beverage that contains ingredients harmful to the body should be avoided.
- ~1972 Priesthood Bulletin
The text of the Word of Wisdom says that, "all wholesome herbs God hath ordained for the constitution, nature, and use of man” (Doctrine and Covenants 89:10). The word wholesome is an important keyword, and Mormons are counseled to consider the things they take into their bodies as to whether they are wholesome or not. The scripture continues, “All these to be used with prudence and thanksgiving” (Doctrine and Covenants 89:11). The idea of prudence is also important. Candy and sweets are not forbidden by the Word of Wisdom either, but it is wise and prudent to eat these sparingly. Caffeine is addictive, and while avoiding it has never been a commandment in Mormonism similar to the prohibition against alcohol, nevertheless, Mormons have been counseled to avoid it.
Caffeine is most harmful because it is addictive. Avoiding addiction so that one has control over his body is one of the underlying principles of the Word of Wisdom. For this reason, it is wise to avoid eating too many foods or drinks that have caffeine in them. However, the choice is individual. Most people feel that they can drink a caffeinated soda or eat a chocolate every once in a while, but do not feel it is prudent to have these things on a daily basis. Church-owned schools refrain from selling caffeinated beverages in their cafeterias.
Special vigilance is now required of Latter-day Saints, since super-caffeinated "energy drinks" have hit the marketplace, some containing alcohol. The Word of Wisdom was given because of "conspiring men in the last days," and such men have conspired to hide ingredients with ambiguous labeling of dangerous drinks.
- The Word of Wisdom by Lance Starr -- FAIR LDS