Spearmint, so named for its long pointed leaves, is an herb native to Europe and Southwest Asia, and widely grown in the north central United States. Known for its mild taste, spearmint is a favorite ingredient in various candies, gum, and drinks such as the mojito and the mint julep.
Some medicinal uses of spearmint include the treatment of stomach pain and gas, and the treatment of excessive hairiness (hirsutism) in women. It also seems to have excellent antioxidant properties, as well as a relaxation effect in aromatherapy. Topical application of spearmint can be effective to reduce pain and inflammation related to arthritis, toothache, and other conditions.
Peppermint is a hybrid species, created when spearmint was crossed with watermint. It has a sharper taste than peppermint, but has similar uses as a flavoring agent and in aromatherapy.
Peppermint's medicinal properties seem to be more pronounced than those of spearmint. It has stronger effects on stomach upset, including as a very promising treatment for Irritable Bowel Syndrome (IBS). It also shows protective effects on the bodies of those going through radiation treatment for cancer.
Peppermint can be toxic in high doses, causing stomach upset and increased acid production, and is a potential liver toxin. Spearmint, on the other hand, appears to be safe in oral and topical applications.