Peppermint is an effective remedy for an upset stomach or nausea, but can actually make heartburn and gastroesophageal reflux disease (GERD) worse. “It relaxes the muscle that keeps the stomach contents from washing back up into the esophagus. It would tend to make heartburn worse,” says Phil Hagen, M.D. medical editor-in-chief of The Mayo Clinic Book of Home Remedies. An alternative to peppermint is ginger, which can also alleviate an upset stomach or nausea.