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Grey tongue differs in yin and yang patterns. If cold pathogen directly invades the yin meridians, the tongue will immediately appear grey-black without accumulated coating. If heat transmits to the three yin meridians, it must be after four or five days when exterior symptoms have ceased and the coating turns grey. The grey color may appear at the root, tip, or center, or the entire tongue may be uniformly grey-black. Generally, if it is a heat syndrome transmitted through the meridians, there will be a dry grey-black coating, which should be treated with purgation to drain heat. If it is a direct invasion of the three yin meridians presenting as grey-black without coating, warming the meridians and dispersing cold should be employed. There is also blood stasis syndrome, where the patient acts like they are mad, or closes their eyes and speaks deliriously; some do not act mad nor speak, losing consciousness, yet have a dark face and grey tongue. One must assess the severity to purge the blood. Do not mistakenly give cold water, as this may guide the failed blood into the heart, leading to untreatable conditions.

Pure Grey Tongue
A grey tongue without coating indicates direct invasion of the three yin meridians complicated by cold food retention. The pulse must be deep, fine, and slow. With no thirst and no irritability, Fuzi Lizhong Tang (Aconite Root and Poria Decoction) and Sini Tang (Recovery from Reversal Decoction) are used for rescue. On the next day, if the tongue shows slight yellow within the grey, life is preserved; if it gradually shrinks, dries, and turns black, death ensues.

Grey Center Tongue
Grey color appearing in the center, accompanied by excessive thirst, qi rushing up to the heart, hunger without desire to eat, and vomiting roundworms upon eating, indicates heat transmitting to the Jueyin meridian. Wumei Wan (Mume Pill) is the primary formula.

Grey-Black Dry Coated Tongue with Cracks
When Earth pathogen overcomes Water, the tongue appears grey-black with cracks. Liangge San (Cool the Chest Powder) or Tiaowei Chengqi Tang (Regulate the Stomach and Direct to the Interior Decoction) can be used for purgation. Two or three out of ten may be saved. If after purgation, thirst persists and fever does not subside, it is untreatable.

Grey Root, Yellow Tip, Red Center Tongue
The root is grey, the center red, and the tip yellow, indicating dryness-heat in the intestines and stomach. If there is extreme thirst, delirium, no bowel movement for five or six days, and passing gas, purgation is indicated. If it is a warm disease or heat disease with aversion to cold and floating pulse, choose Liangge San or Shuangjie San (Double Resolution Powder).

Grey Tongue with Concentric Halos
This is plague disease with heat toxin transmitting throughout the three yin meridians. Each time heat toxin transmits inward, a layer of grey halo appears on the tongue. Due to abundant toxin, multiple halos form. This is a critical condition; urgently use Liangge San and Shuangjie San to resolve toxicity, and Chengqi Tang to purge. One halo is mild, two are severe, and three indicate certain death. There are also cases with two or three layers of horizontal lines, similar to these concentric halos.

Grey-Black Tongue with Dry Spines
A grey-black tongue with dry spines, accompanied by dry throat, dry mouth, wheezing, and chest fullness, indicates evil heat knotting in the Shaoyin meridian. Purgation is required, but one must wait until the patient passes gas before purging. If purged too early, it causes difficulty in urination.

Grey-Black Tip Tongue
After sweating has resolved the exterior, if the tongue tip appears grey-black, it is due to retained food not yet digested, or re-injury from diet causing resurgence of evil heat. Tiaowei Chengqi Tang is used for purgation.

Grey-Black Dry Spined Tip Tongue
The tongue tip is grey-black with spines and is dry, caused by consuming food after the onset of illness. Although symptoms include deafness, hypochondriac pain, fever, and bitter taste, Xiaochaihu Tang (Minor Bupleurum Decoction) must not be used. Daxiehu Tang (Major Bupleurum Decoction) or Tiaowei Chengqi Tang added with digestive-resolving herbs must be used to achieve efficacy.

Grey Center with Ink-Smooth Tongue
In the faint grey center, there are four or five spots of smooth coating resembling ink. This indicates heat pathogen transmitting inward with retained food not yet transformed. Dachaihu Tang (Major Bupleurum Decoction) is used.

Grey-Black with Much Yellow and Little Root Tongue
The tongue is grey with a yellow root, indicating heat transmitting to Jueyin with stagnation in the stomach. In Shanghan (Cold Damage), if after six or seven days without diarrhea, sudden fever occurs with diarrhea and unceasing sweating, death results due to collapse of healthy qi.

Grey Edges with Purple Center Tongue
The edges of the tongue are grey-black while the center is pale purple. The patient occasionally bites the tongue tip for relief. This indicates Shaoyin jue qi (rebellious qi) rising upward; it is not treatable with medicine.