According to http://www.organicfacts.net:
“The health benefits of Spearmint Essential Oil can be attributed to its properties as an antiseptic, antispasmodic, carminative, cephalic, emenagogue, insecticide, restorative and stimulant substance.
The Essential Oil of Spearmint is extracted by steam distillation of flowering tops of the spearmint plant, whose scientific name is Mentha Spicata. The main components of this oil are Alpha Pinene, Beta Pinene, Carvone, Cineole, Caryophyllene, Linalool, Limonene, Menthol and Myrcene.
Although its aroma is similar to that of peppermint, due to the presence of menthol, its menthol content is negligible as compared to that of peppermint oil. Spearmint oil has been a substitute for peppermint when it is unavailable, and possesses similar medicinal properties, due to the presence of similar compounds in its essential oil. Instances of its use in ancient Greece have even been found in historical records.
The health benefits of peppermint oil include its ability to treat indigestion, respiratory problems, headache, nausea, fever, stomach and bowel spasms, as well as for pain relief. Due to the presence of menthol, menthone and menthyl esters, peppermint and peppermint oil find wide applications in the manufacturing of soap, shampoo, cigarettes, toothpaste, chewing gum, tea and ice cream.
Peppermint is a cross between watermint and spearmint and is native to Europe. Historically, the herb has been known for its medicinal uses, and its impressively long history often gives it the prestigious title as the world’s oldest medicine.
Unlike many other herbs and essential oils, numerous health benefits of peppermint and peppermint oil have been studied and proved by the scientific community. As a result, peppermint oil is also sold in the form of capsules and tablets, and is even prescribed by doctors of alternative and modern medicine.
Peppermint oil can also be used as a flavoring agent. You will find very few people who find peppermint unsuitable to their palate. Peppermint oil contains numerous minerals and nutrients including manganese, iron, magnesium, calcium, folate, potassium, and copper. It also contains omega-3 fatty acids, Vitamin A and Vitamin C.
Few Words of Caution: There are no reported dangers of using Spearmint essential oil, but as an emenagogue, it should not be taken by pregnant women.
There are some risks in using too much peppermint oil, including allergic reaction, heartburn, and headaches. Basically, the same rules apply to using peppermint oil as to any other alternative supplement or dietary change; speak to a doctor, and if you don’t consult a professional, start with small topical doses or skin patch tests to see how it affects your system.”