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It’s a combination of 小柴胡汤 and 小承气汤. So it deals with a mixed exterior-interior pattern, but at the same time the problem of a replete viscera (阳明腑实证). Rightfully, if you have a mixed exterior-interior pattern, precipitation (fecal excretion) is contraindicated. However…

《医方集解》：“少阳固不可下，然兼阳明腑实则当下。”

Which means to say that if it were just a 少阳 pattern alone, you don’t precipitate, but if accompanied by a 阳明腑实 pattern, it’s fine. To me, this is an oft-repeated theme in chinese medicine: theory lumps upon theory. the old theories remain, but exceptions are created upon them. Some theories would aver that 少阳 is what comes after 阳明, hence making them two distinct phases in an illness continuum. All of a sudden they both happen at the same time, and so the theory makes compensation.

I’d rather see them as categories that describe a certain set of illness manifesations. For example, with 少阳，it’s 往来寒热，胸胁苦满，默默不欲饮食 etcetera; and with 阳明, it’s mainly your fecal matter not getting through. So, I’d put aside the phasal theory for now, and just observe here that 张仲景 is adding herbs to address additional symptoms.

As for the prescription, here’s my song:

• 大柴胡汤黄芩藏
• 姜夏枣芍枳大黄
• 少阳不可下然兼
• 阳明腑实则当下

Compared to 下柴胡汤:

1. the first line’s herbs are the same: 柴胡、黄芩.
2. the second line has 姜、夏 but no 枣、人. Instead, it’s 枣、芍.
   1. and there’s no 甘草; rather, its 枳大黄.

So, my analysis of it sees:

1. 柴胡 as usual.
2. 辛开苦降 in 夏、姜、芩.
3. 枣 no longer has its tonifying groupies 人参 and 甘草.
4. 枳实 and 大黄 are added as representatives from 小承气汤.
5. and there’s 芍药 to 缓急止痛.

It’s eight herbs instead of seven in 小柴胡汤.

I remember it as being used nowadays for acute pancreatitis, acute gall bladder inflammation, gall stones. Not looking at the research in detail yet, but understand that precipitation is very important for pancreatitis, while there must be components (or by-products of component interactiosn) in there, 柴胡 included, that ameliorate the gall bladder issue.