According to the United States Pharmacopeia1 methyl salicylate (oil of gaultheria, oil of wintergreen, oil of betula or oil of sweet birch) is a colorless, yellowish or reddish liquid having the characteristic odor and taste of gaultheria. It can be made synthetically or by distillation with steam from the leaves of Gaultheria procumbens or Betula lenta. The law requires that the label show the source of the product but not its toxic qualities. This oil is dispensed freely as a counterirritant and is also occasionally prescribed in very small doses for internal use. It is the main constituent of some of the "patent medicines" sold for the treatment of rheumatism.
While standard textbooks give only brief mention to methyl salicylate poisoning, nevertheless the symptoms and pathology have been adequately described.2 Twenty-eight cases of methyl salicylate poisoning due to ingestion were reviewed by Lawson and Kaiser,3 who added
Baxter EH, Hartwell RM, Reck LE. METHYL SALICYLATE POISONING. JAMA. 1938;111(27):2476–2477. doi:10.1001/jama.1938.72790530004009b