I was wondering why do people take peppermint oil capsules?

Relax the esophagus: It can be used to relieve the feeling of fullness after a large meal-like a peppermint is given in some restaurants. In theory, the esophagus relaxes, one can "eructate" (burp) and then feel less full.

Several uses: Peppermint oil has multiple uses. A very popular one is for irritable bowel syndrome (ibs). http://tinyurl.com/kjesndd it can also help with indigestion. Peppermint oil can be used topically to help abdominal distension, antispasmodic in UGI endoscopy, headaches including migraine, and postherpetic neuralgia. A dilution is used in these latter situations.