The Spirit of the Word of Wisdom

"Obviously the standard of judgment must be uniform throughout the Church, and local offices are not at liberty to add other items to this list.  However, there are many other substances which have a harmful effect on the human body, though such particular things are not specifically prohibited by the Word of Wisdom.  Certainly the partaking of cola drinks, though not included within the measuring standard here set out, is in violation of the spirit of the Word of Wisdom.  Harmful drugs of any sort are in a like category."
 

-Bruce R. McConkie, Mormon Doctrine, p. 845