Dosage is related to the following factors: 

Property: Moderate and bland substances are prescribed in a larger dosage, while strong-flavored or toxic substances are prescribed in a smaller dosage. Flowers and leaves of light weight are prescribed in a relative small dosage. Heavy and nontoxic minerals and shells are often prescribed in a larger dosage. Invaluable substances are usually prescribed in a small dosage. 

Substance combinations and drug forms: If a medicinal substance is used alone, a large dosage is needed.  If it is in a complex formula, the dosage of each ingredient is small.  In a complex formula if one substance is used as the sovereign ingredient, its dosage is larger than when it is used as an adjuvant ingredient.  Dosage varies in different drug forms, e.g. larger dosage is needed in decoctions than in pills and powders. 

Severity of disorders, physical state and age: In general, for mild and chronic diseases, small dosage is used, but for severe and acute diseases, larger dosage is used. For weak patients, the elderly and infants, small dosage is used, and for strong patients, larger dosage is used. 

Besides, individual differences, climate, season and regional variations should be taken into consideration.