What’s wrong with the thick white tongue coating after taking Zhi Bai Di Huang Wan?

The appearance of thick white tongue coating on taking Zhi Bai Di Huang Wan may be due to weakness of the spleen and stomach or prolonged use of the medicine.
Zhi Bai Di Huang Wan is a proprietary Chinese medicine composed of Zhi Mu, which nourishes yin and moistens dryness (nourishes yin essence and removes heat), Huang Bai, which clears heat and dries dampness, Radix Rehmanniae Praeparata, which tonifies blood and nourishes yin, Cornu Cervi Pogostemon, which tonifies liver and kidneys, Mudan Pi, which clears heat and cools the blood, Chinese yam, which nourishes qi and nourishes yin, Poria, which strengthens the spleen and seeps out dampness, and Ze Xue Di, which induces diarrhea to relieve heat, which are all in the prescription, and together they play a role of nourishing yin and lowering the effect of fire.
This product is mainly used in treating the symptoms of yin deficiency and fire exuberance, such as low fever in the afternoon, heartburn, sweating of hands and feet, night sweating, dry mouth and sore throat, tinnitus, lumbago, spermatorrhea, and short and yellow urine.
This product should be taken with caution by pregnant women. It is not suitable for patients with deficiency cold disease, which is characterized by fear of cold, cold hands and feet, and preference for hot drinks. It should not be taken at the same time with cold and flu medicines. This product should be taken on an empty stomach or before meals with boiled water or lightly salted water. If the symptoms do not improve after one week of taking the medicine, you should go to the hospital.
As Zhi Bai Di Huang Wan contains Radix Rehmanniae Praeparata, Rhizoma Dioscoreae, Rhizoma Dioscoreae, Cornu Cervi Pantotrichum and other nourishing ingredients, prolonged use of the medicine by those with weak spleen and stomach may aggravate the weakness of the spleen and stomach and breed internal dampness, resulting in thick white tongue coating. It is recommended to stop the medication and seek medical attention to avoid delaying the condition.