Mu Zei — Winter horsetail

Combinations & formulas

• Ju Hua (Chrysanthemum flower) — for red, watery eyes caused by wind and heat: Ju Hua also cools and clears the Liver meridian and enhances the eye-clearing effect.
• Sang Ye (Mulberry leaf) — for burning eyes and sensitivity to light caused by wind-heat: Sang Ye dispels wind-heat from the Upper Burner and helps cool the eyes.
• Bai Ji Li (Field Speedwell fruits) — for blurred vision and corneal opacities: Bai Ji Li dispels liver wind and clears the vision while simultaneously promoting the rise of liver yang.
• Jue Ming Zi (Cassia seeds) — for chronically red eyes associated with liver heat and constipation: Jue Ming Zi nourishes the liver, calms the yang, and directs heat downward.
• Man Jing Zi (Keuschlamm–Fruits) — for headaches accompanied by eye discomfort caused by wind-heat: Man Jing Zi dispels wind-heat from the head and enhances the clearing effect on the eyes.
• Gou Qi Zi (Goji berry) — for Yin deficiency with blurred vision and a sensation of dryness in the eyes: Gou Qi Zi nourishes Liver Yin and balances the cooling effect of Mu Zei.

History & Tradition

Mu Zei — the Winter horsetail (Equisetum hiemale) — is one of the oldest vascular plants on Earth. The class Equisetopsida was already established over 300 million years ago in prehistoric times, when tree-sized relatives dominated the Carboniferous coal forests. What grows today as a delicate, knotty herb along the roadside is a living fossil—morphologically virtually unchanged since the Paleozoic Era. For ancient Chinese physicians, this consistency was no coincidence: a plant that survives for millions of years must possess a special inner strength.

In classical TCM literature, Mu Zei is primarily discussed in relation to the Liver meridian and the eyes. The Ben Cao Gang Mu Li Shizhen’s 16th-century *Bencao Gangmu* describes Mu Zei as a remedy for pterygium—those tissue growths on the cornea that cloud vision—as well as for redness, tearing, and sensitivity to light in the eyes. The plant was considered a „cleanser of the window of the eye,“ since in TCM the liver and the eyes form an inseparable pair: what harms the liver clouds the vision; what clears the liver restores the eyes’ radiance.

The Western name is particularly interesting: Horsetail or horsetail—named for its high silica content, which craftsmen used in the past to polish metal and sand wood. TCM practitioners understood this „sanding herb“ of the carpenters in exactly the same way: It “smooths away” the opacities of the cornea and restores clarity to the window of the eye. The parallel between Western folk medicine and the Eastern TCM tradition is unusually direct here—a rare testament to universal knowledge of plants across cultures.

In Japan, a related tradition of use is practiced under the name Tokusa (木賊), where horsetail grows as a sacred plant at temples and is used for purification rituals. In ancient China, Mu Zei was harvested in late summer, when the stems had reached their greatest strength and silica content—a rhythm that embodies the close connection between harvest time and medicinal efficacy in classical herbalism.

Contraindications & caution

Do not use in cases of Qi deficiency without signs of heat. Use with caution in cases of severe Yin deficiency, as Mu Zei has a drying effect and may further weaken existing Yin. Mu Zei is contraindicated in cases of blood deficiency with a sensation of dry eyes, blurred vision without signs of wind-heat, and impaired night vision—in these cases, the nourishing root is lacking, and a clearing herb would exacerbate the deficiency. For chronic eye conditions such as glaucoma, macular degeneration, or retinopathy, Mu Zei alone is not suitable—these conditions require nourishing and supportive therapies, not pure clearing. Pregnancy: Not recommended — there is insufficient safety data; use only after carefully weighing the benefits and risks and consulting with an experienced TCM practitioner. Renal insufficiency: Use with caution due to its diuretic effect and the potential for increased silica load in patients with impaired renal function; contraindicated in patients with advanced renal insufficiency. Thiaminase Note (Western): Equisetum hyemale has weaker thiaminase activity than, for example, E. arvense or E. palustre, but could theoretically affect vitamin B1 levels with long-term use or at high doses. If relevant risk factors are present (malnutrition, alcohol dependence), ensure an adequate intake of vitamin B1. Drug Interactions: May increase the effects of diuretic medications; consult a doctor if taking diuretics, lithium, or cardiac glycosides at the same time.

Processing

The processing of Mu Zei follows traditional TCM drying principles: The goal is to preserve the silica structures and heat-sensitive flavonoids while reducing the moisture content to less than 12 %. For topical eye preparations, additional purification steps are essential to eliminate particles and microbial contamination.

• Standard drying (raw drug)
  1. Cut the stem just above the ground — leave the rhizome intact
  2. Wash thoroughly under clean running water; remove dirt and debris
  3. Bundle and dry in the shade (not in direct sunlight—this prevents flavonoid degradation); at 35–45 °C
  4. Dry to a residual moisture content of <12 %; the finished drug is stiff and breaks cleanly
  5. Store in airtight containers in a cool, dry place
• Preparation of an Eye Solution (Decoction for Eye Irrigation)
  1. Add 10–15 g of dried Mu Zei to 300–400 ml of water
  2. Simmer for 20–30 minutes (do not let it boil vigorously)
  3. Double filtration: first through a fine sieve, then through sterile gauze or a coffee filter—remove all particles!
  4. Allow to cool to body temperature (36–37 °C) before use
  5. Consume within 24 hours; do not store

Comparable western herbs

• Eyebright (Euphrasia officinalis) — The classic European eyebright. Similar to Mu Zei in cases of wind-heat, eyebright has anti-inflammatory and astringent effects on eye tissue; it has been used in folk medicine for centuries to treat red, watery, and irritated eyes. Astringent tannins and aucubin are its main active ingredients; initial clinical evidence suggests efficacy in treating allergic conjunctivitis.
• Cornflower (Centaurea cyanus) — Traditionally used as an eye wash for conjunctivitis and eye strain. The flower extracts contain anti-inflammatory flavonoids and anthocyanins that can protect the capillaries in the eyes. In Central European folk medicine, it is a direct counterpart to Mu Zei’s clarifying and cooling effect.
• Bilberry (Vaccinium myrtillus) — Rich in anthocyanins, which improve microcirculation in the retina and cornea; well-documented for supporting visual acuity and dark adaptation. Serves as a Western counterpart to Mu Zei in cases where eye symptoms are to be treated by improving blood circulation—complements Mu Zei’s dispersing effect.
• Marigold (Calendula officinalis) — Anti-inflammatory and antibacterial for eye irritation and superficial inflammation; used as an eye compress or rinsing solution. It shares with Mu Zei the clarifying and anti-inflammatory properties for external eye conditions, but has a more warming and drying effect and is less focused on wind-heat patterns.