English Pennyroyal (Mentha pulegium): Traditional Herb with Toxic Oil

English Pennyroyal: The Mint That Repels Fleas but Demands Respect

English pennyroyal (Mentha pulegium) is a low-growing, creeping mint with small, oval leaves and whorls of lilac flowers. It has a strong, spearmint-like scent and a long history as a flea repellent and emmenagogue, but its essential oil (pulegone) is highly toxic to liver and can be fatal.

Botanical Profile

Native to Europe, North Africa, Middle East. Grows 6–12 inches tall, spreading by stolons. The leaves are smaller than other mints. Flowers in summer.

Historical Uses and Severe Cautions

• Flea repellent: Fresh or dried stems in pet bedding (external only).
• Traditional medicine: Emmenagogue, abortifacient. Oil is hepatotoxic and neurotoxic; deaths reported. Do not ingest oil. Tea in very small amounts only with expert guidance.
• Groundcover: Tolerates light foot traffic; minty scent when walked on.

Grow in full sun to part shade, moist soil. Can be aggressive. Keep away from children and pets. Do not use essential oil. Hardy in USDA zones 6–9.