Properties & Uses:
The Gaultheria species share the common characteristic of producing oil of wintergreen, the chemical methyl salicylate, which gives plants a distinctive 'medicinal' smell when bruised.
Some species of birch Betula lenta - Sweet Birch or Cherry Birch, also produce oil of wintergreen. Commercial methyl salicylate is now synthesized, and used in many OTC topical pain relief preparations.
Wikipedia
Wintergreen is a powerful and useful oil that I have used with success as a topical analgesic on my tough arthritis pain. Because of the toxicity of methyl salicylate, many aromatherapists do not recommend it's use. However as long as you are not sensitive to salicylates, ( I am not, thankfully since I have arthritis), and you can use it with a dose of common sense and respect for the herb.
Essential Oil
Side Effects: of Wintergreen
Very potent skin irritation. Keep out of reach of children. For external use only. Dilute properly; Avoid if pregnant. Warning: Harmful or fatal if taken internally. As little as one teaspoon can be fatal if ingested by a child. Use sparingly,as the active phytochemical, methyl Salicylate is toxic in large doses.