I preached to a large congregation at the stand, on the science and practice of medicine, and desiring to persuade the saints to trust in God when sick, and not in an arm of flesh, and live by faith and not by medicine, or poison; and when they were sick, and had called for the Elders to pray for them, and they were not healed, to use herbs and mild food. 1
And there were some who died with fevers, which at some seasons of the year were very frequent in the land but not so much so with fevers because of the excellent qualities of the many plants and roots which God had prepared to remove the cause of diseases, to which men were subject by the nature of the climate.
And again verily I say unto you, all wholesome herbs God hath ordained for the constitution, nature, and use of man.
Every herb in the season thereof, and every fruit in the season thereof, all these to be used with prudence and thanksgiving.
Joseph Smith, The Teachings of Joseph Smith, p. 28