A popular flavoring in gum and other candies, peppermint oil actually has a long history of use as a medicine. It has been used primarily to treat gastrointestinal problems such as indigestion. As a supplement, it comes in enteric-coated capsules that prevent the body from breaking it down until it reaches the small intestines. While a generally safe supplement, peppermint oil can cause some side effects, and its use can be inappropriate in certain instances. If you believe taking peppermint oil might address a particular health concern, consult your doctor on whether to use this supplement.

The Beth Israel Deaconess Medical Center states that peppermint oil is generally safe when used appropriately. Like other supplements, however, it can cause stomach upset. The University of Michigan Health System reports that enteric-coated capsules can cause a burning feeling in the rectum.

High doses could cause heart problems, nausea, loss of appetite, loss of balance and other nervous system issues. Large amounts are potentially toxic and can lead to renal failure and death.

Peppermint oil can relax the muscles of the esophageal sphincter, a band of muscles that allows food to pass from the esophagus to the stomach. This loosening can lead to stomach acid refluxing up into the esophagus. Do not use peppermint oil if you suffer from gastroesophageal reflux disease, ulcers, chronic heartburn or hiatal hernia. Use of peppermint oil supplements is also contraindicated if you have liver disease, inflammation of the gallbladder, obstruction of the bile ducts or are pregnant or breastfeeding.

Beth Israel reports peppermint oil supplements can reduce blood levels of the immunosuppressant drug cyclosporine, making it less effective. Drugs.com notes that peppermint oil might interfere with the actions of the enzyme CYP-450, which could affect the metabolization of numerous drugs that require this enzyme. If you take any medications, it is important to clear the use of natural supplements with your doctor.

The University of Michigan advises you to talk to your doctor before using peppermint supplements if you have gallstones. Drugs.com cautions against giving children under 8 enteric-coated peppermint capsules.