Side Effects and Warnings

Peppermint is generally regarded as being safe in non-allergic adults when taken in small doses, for example as tea.

Peppermint oil may be safe in small doses, although multiple adverse effects are possible. When used on the skin, peppermint oil has been associated with allergic/hypersensitivity reactions, skin rash/hives/contact dermatitis, mouth ulcers/sores, chemical burn and eye irritation. Lung injury has occurred following an injection of peppermint oil. Peppermint oil taken by mouth may cause headache, dizziness, heartburn, anal burning, slow heart rate, or muscle tremor. Very large doses of peppermint oil taken by mouth have resulted in muscle weakness, brain damage, and seizure.

Peppermint oil should be used cautiously by people with G6PD deficiency or gallbladder disease. Use in infants or children is not recommended due to potential toxicity.

Menthol, a constituent of peppermint oil that is included in mouthwashes, toothpastes, mentholated cigarettes, and decongestant "rubs" or lozenges, has been associated with multiple adverse effects, such as serious breathing difficulties, asthma, skin bruising (purpura), and mouth sores. Although small amounts may be safe in non-allergic adults, higher doses may be deadly in humans or cause brain damage. Use on the skin may also cause rash, severe skin damage (necrosis), or kidney damage (interstitial nephritis). Inhalation of large doses of menthol may lead to dizziness, confusion, muscle weakness, nausea, or double vision.