Peppermint (Mentha piperita L.) is one of the most widely consumed single ingredient herbal teas.    Medical research shows that peppermint oil can reduce spasm of smooth muscle (the type of muscle that comprises the esophagus, stomach, lungs, intestines) and can therefore provide some relief for conditions like IBS (irritable bowel syndrome), esophageal spasm, and spastic colon.  In lab tests, peppermint  has significant antimicrobial and antiviral activities, strong antioxidant and antitumor actions, and some antiallergenic potential.

Animal model studies demonstrate a relaxation effect on gastrointestinal (GI) tissue, analgesic (pain reducing) and anesthetic (nerve desensitizing) effects in the central and peripheral nervous system, immunomodulating actions and chemopreventive potential.

The effects of peppermint oil and eucalyptus oil preparations on headaches and cognitive function were investigated in 32 healthy subjects in a double-blind, placebo-controlled, randomized cross-over design.* Four different test preparations were applied to large areas of the forehead and temples using a small sponge and their effect was evaluated by comparing baseline and treatment measure. The combination of peppermint oil, eucalyptus oil and ethanol increased cognitive performance and had a muscle-relaxing and mentally relaxing effect, but had little influence on pain sensitivity. A significant analgesic effect with a reduction in sensitivity to headache was produced by a combination of peppermint oil and ethanol (rubbing alcohol). The essential plant oil preparations often used in empiric medicine can thus be shown by laboratory tests to exert significant effects on mechanisms associated with the pathophysiology of headache.

The evidence suggests that peppermint can somehow relax smooth muscle.  Since blood vessels are also comprised of smooth muscle, and some types of headaches are caused by spasms in the blood vessels that lead to the head, taking peppermint either as a tea or concentrated oil may provide relief.

*Göbel H, Schmidt G, Soyka D, Effect of peppermint and eucalyptus oil preparations on neurophysiological and experimental algesimetric headache parameters.  Cephalalgia. 1994 Jun;14(3):228-34; discussion 182.