Drugs are of two kinds: medicinal/therapeutic or narcotic/hallucinogenic/habit-forming. The Church of Jesus Christ of Latter-day Saints does not object to medicine necessary to help bodies heal, live, or function in a normal, healthy way. Everything in the doctrine of the Church supports the health of the individual and condemns that which will harm or corrupt. Specifically, the Word of Wisdom stresses the importance of keeping the body healthy and treating it as a temple of God.
Word of Wisdom
Early in 1833, Joseph Smith received a revelation for the health of members of the Church for “the temporal salvation of all the saints in the last days” (Doctrine and Covenants 89:1). Mormons point to this revelation as proof that Joseph Smith was a prophet, because long before medical science proclaimed the harmful effects of alcohol and tobacco, Mormons were warned against consuming them. Long before medical science cautioned the public to avoid caffeine in their diets, Mormons had stopped drinking coffee and tea. Long before medical science understood the dangers of high fat, heavy meat diets with cholesterol, Mormons were cautioned to “eat [meat] sparingly.” Long before medical science understood the importance of eating whole grains and many servings of fruits and vegetables, Mormons were encouraged to eat them. And even before medical science announced that fresh-picked fruit and vegetables contained more vitamins and minerals, Mormons were encouraged to eat fruit “in the season thereof.” So it's not surprising that many Mormons strongly believe in the Word of Wisdom. Following it has made Mormons among the healthiest people in the world.
Though not specifically mentioned in the Word of Wisdom, the use of illegal, or unnecessary legal, narcotics and hallucinogens and other harmful substances are against the spirit of the Word of Wisdom. Mormons have been commanded in modern days not to use them because consuming anything—just as doing anything—that hinders the Holy Ghost from being with them or hurts them in any way is not pleasing to God. The former prophet, Gordon B. Hinckley, said,
- I am convinced that [drug] use is an affront to God. He is our Creator. We are made in his image. These remarkable and wonderful bodies are His handiwork. Does anyone think that he can deliberately injure and impair his body without affronting its Creator? . . . Can anyone doubt that the taking of these mind- and body-destroying drugs is an act of unholiness? Does anyone think that the Spirit of God can dwell in the temple of the body when the body is defiled by these destructive elements? . . God grant you the strength to stand free from this enslavement and from the personal holocaust of destruction which inevitably follows. 
Drug users will not be in a condition in which the Holy Ghost can readily work with them, so they lose the protection, guidance, comfort, and knowledge the Holy Ghost provides. Boyd K. Packer, a Mormon apostle, said,
- If we abuse our body with habit-forming substances, or misuse prescription drugs, we draw curtains which close off the light of spiritual communication. Narcotic addiction serves the design of the prince of darkness, for it disrupts the channel to the holy spirit of truth. . . . Addiction has the capacity to disconnect the human will and nullify moral agency. It can rob one the power to decide. 
Mormons have many experiences that convince them of the importance of the presence of the Holy Ghost for their safety and welfare. To them, taking anything into their bodies that repels the Holy Ghost is like taking off a bullet-proof vest in a war zone.
Russell M. Nelson, an apostle who is also a physician, states that,
- The noble attributes of reason, integrity, and dignity, which distinguish men and women from all other forms of life, are often the first to be attacked by drugs and alcohol. . . .We are free to take drugs or not, But once we choose to use a habit-forming drug, we are bound to the consequences of the choice. Addiction surrenders later freedom to choose. Through chemical means, one can literally become disconnected from his or her own will! 
Mormons understand that repentance can bring them back from final destruction, but that, if they do unwise things, they'll still have consequences to face. They watch with apprehension and concern as others take harmful substances into their bodies, knowing that addiction, loss of all they own or love, withdrawal, and rehabilitation are all painful.
Mormons believe that Lucifer and his cohorts envy the bodies that Mormons and other people on earth have gained from their obedience during the War in Heaven. As the New Testament shows, these devils want bodies so much, they're willing to enter even the bodies of pigs. So it's no wonder that Lucifer delights when people with bodies defile them and turn them over to his influence and use. Wise Mormons choose not to hand over their bodies and agency to someone who has always sought their destruction.
Drug use hurts people's health, addicts and controls them, and sometimes even kills them. Harmful drug use also yields other frequent results: violence, spouse and child abuse, crime and prison, prostitution, loss of job and financial ruin, loss of reputation and social standing, homelessness, and divorce. Church members who use illegal substances or misuse legal substances won't receive a temple recommend (permission to enter the temple). They may also lose their membership until they repent and change their self-destructive behaviors. These chastisements are meant for correction, not condemnation, because the gospel's purpose is to help people be happy and progress as far as they can.
When approached by addicted members for help, Church leaders help them seek professional rehabilitation and support their recovery with counsel. Addicted members and their families, even without bishop referral, can also go to the LDS Family Services website to find the nearest LDS Family Service office near them. They are located throughout the United States, as well as in Canada, England, Australia, New Zealand, and Japan. Mexico also has a new office that is gradually setting up various services. These offices provide out-patient services for a fee (in the U.S., approximately $60-70 a session of 50 minutes). Occasionally, members who cannot afford fees may be fortunate enough to have them waived, if qualified professional counselors who are members of their stake will counsel them privately. Also available free to addicts are addiction support groups based on the 12-step program. Most of the LDS Family Services offices have these support groups connected with them. The support groups can be located on the website. Along the Wasatch front in Utah, the families of addicts also have formed family support groups.
The best advice Mormon Church members receive is to never try "recreational" drugs or alcohol even once. In some cases, once is all that's necessary to cause addiction, permanent damage, or death. Teenagers are advised to avoid social situations where drug use or drinking occurs. They are also cautioned to carefully choose their friends so that they're not tempted or drawn into risky situations.
- Gordon B. Hinckley, “The Scourge of Illicit Drugs,” Ensign, Nov 1989, 48.
- Boyd K. Packer, “Revelation in a Changing World,” Ensign, Nov 1989, 14.
- Russell M. Nelson, “Addiction or Freedom,” New Era, Sep 1989, 4.