Dual-action formulas are further divided into three types depending on the specific situation of simultaneous exterior and interior involvement:

Chapter 4: Dual-Action Formulas for Exterior and Interior

When the illness affects the exterior, use methods of inducing perspiration; when it affects the interior, use methods of purging, descending, or warming; when it affects the semi-exterior, semi-interior region, use methods of harmonization. But what if the illness affects both the exterior and interior simultaneously? In such cases, treating only the exterior will leave the interior diseased, while treating only the interior will fail to resolve the exterior symptoms. Therefore, physicians have devised dual-action formulas that treat both the exterior and interior at the same time. Any formula that has the effect of treating both the exterior and interior is called a dual-action formula.

Dual-action formulas are further divided into three types depending on the specific situation of simultaneous exterior and interior involvement:

② Only by clearly distinguishing between the cold, heat, deficiency, and excess patterns of both the exterior and interior can one determine which type of dual-action formula to use. ③