Black Catechu Classic Formulas — Natural Herb Library

Primary Actions

Stops bleeding while promoting tissue regeneration - classically valued for bleeding traumatic wounds, ulcerated sores, and lesions that need both hemostasis and new flesh generation.
Astringes sores and dries damp ooze - used externally for eczema, weeping skin lesions, oral ulceration, and chronic ulcers with seepage or delayed closure.
Invigorates Blood and reduces trauma swelling - applied in powders and trauma formulas when bruising, swelling, and local injury coexist with active oozing or slow healing.
Can clear phlegm-heat and relieve mouth-throat irritation in small internal doses - a lesser but recognized use when its cool astringent nature is matched appropriately.

Qi Li San (七厘散) - classic trauma powder in which Er Cha helps stop bleeding and promote tissue repair alongside stronger Blood-moving medicinals.
Long Gu Er Cha San (龙骨儿茶散) - external powder tradition for damp weeping eczema and ulcerative skin lesions, using the astringent drying and healing actions of Er Cha.

TCM Wiki lists Er Cha as bitter, astringent, and lightly cold, with the core actions of treating trauma, stopping bleeding, promoting regeneration, and healing wounds.
Me and Qi notes that the Chinese Pharmacopoeia source is black catechu from Acacia catechu, while also warning that other trade materials called catechu are not identical.
The herb is often used interchangeably in trade under names such as Hai Er Cha or Hei Er Cha, but this file keeps the core pharmacopeial name Er Cha.