Inclusion Criteria:
* Age from 18 to 65 years;
* Eligible for the Diagnostic and Statistical Manual of Mental Disorders, 5th edition, criteria for insomnia disorder. The criteria include having difficulties in falling asleep, difficulties in staying asleep, or early morning awakening with clinically significant consequences for daily life for at least 3 nights per week for at least 6 months;
* Insomnia Severity Index (ISI) total score of at least 8 indicating insomnia at the clinical level;
* Diagnosed to be Yin deficiency-induced internal heat pattern according to traditional Chinese Medicine (TCM) theory;
* Able to complete questionnaires and take medications as scheduled; and
* Voluntary written consent.
Exclusion Criteria:
* Known nervous system disease (eg, stroke, Parkinson's Disease);
* Known mental disorders (eg, depression or anxiety) or HADS score 11 or above in any either item;
* Known sleeping related diseases (eg. sleep apnea, nocturnal myoclonus, restless legs, severe nocturnal enuresis or narcolepsy) that may affect the sleeping quality;
* Known pharmacologically induced insomnia;
* With symptoms that significantly disturb sleep such as pain, fever, diarrhea, frequent micturition, and cough;
* Know treatment to comorbid sleep disorders, such as sleep apnea or narcolepsy;
* Work on shift or on night shift;
* Concomitant pharmacological treatment or herbal medicines for insomnia within the past month;
* Known severe medical conditions, such as cardiovascular, liver, kidney or hematopoietic system disease, diabetes mellitus, cancers, cerebrovascular diseases;
* Impaired hematological profile and liver / renal function exceeds the upper limit of the reference value by 2 times;
* Known alcohol and / or drug abuse;
* Known allergic history to any Chinese herbal medicines;
* Diagnosed to be deficiency of spleen according to TCM theory;
* Any contraindications for taking Chinese medicines in the opinion of the investigators;
* Know pregnant or lactating; and
* Involved in other interventional clinical studies at the same time.
