以上所论伤寒太阳篇，诸方虽不一致，大抵皆治太阳在经之
病者也。至治太阳在府之病其方原无多，而治太阳府病之至剧者，则桃核承气汤是也。试再进而详论之。
《伤寒论》原文∶太阳病不解，热结膀胱，其人如狂，血自
下，下者愈。其外不解者尚未可攻，当先解其外。外解已，但少腹急结者，乃可攻之，宜桃核承气汤。
【桃核承气汤方】桃仁五十个去皮尖，桂枝二两去皮，大黄四两去皮，芒硝二两，甘草二两炙。
上五味，以水七升，煮取二升半，去滓纳芒硝，更上火微沸，下火，先食温服五合，日三服，当微利。
此证乃外感之热，循三焦脂膜下降结于膀胱，膀胱上与胞室
之脂膜相连，其热上蒸，以致胞室亦蕴有实热血蓄而不行，且其热由任脉上窜，扰乱神明，是以其人如狂也。
然病机之变化无穷，若其胞室之血蓄极而自下，其热即可随血而下，是以其病可愈。若其血蓄不能自下，且
有欲下不下之势，此非攻之使下不可。惟其外表未解，或因下后而外感之热复内陷，故又宜先解其
外表而后可攻下也。
大黄∶味苦、气香、性凉，原能开气破血，为攻下之品，然无专入血分之药以引之，则其破血之力仍
不专，方中用桃仁者，取其能引大黄之力专入血分以破血也。徐灵胎云∶桃花得三月春和之气以生，而花色
鲜明似血，故凡血郁、血结之疾，不能自调和畅达者，桃仁能入其中而和之散之，然其生血之功少，而去瘀之
功多者何也？盖桃核本非血类，故不能有所补益，若瘀血皆已败之血，非生气不能流通，桃之生气在于仁，而
味苦又能开泄，故能逐旧而不伤新也。至方中又用桂枝者，亦因其善引诸药入血分，
且能引诸药上行以清上焦血分之热，则神明自安而如狂者可愈也。
特是，用桃核承气汤时，又须细加斟酌，其人若素日少腹恒觉 胀，至此因外感之激发，而 胀益甚
者，当防其素有瘀血，若误用桃核承气汤下之，则所下者，必紫色成块之血，其人血下之后，十中难救一二。
若临证至不得已必须用桃核承气汤时，须将此事帮助以免病家之误会也。
热结膀胱之证，不必皆累及胞室蓄血也。人有病在太阳旬余不解，午前稍轻，午后则肢体酸懒、头
目昏沉、身似灼热、转畏寒凉、舌苔纯白、小便赤涩者，此但热结膀胱而胞室未尝蓄血也。此当治以经府双
解之剂，宜用鲜白茅根锉细二两，滑石一两，共煮五六沸取清汤一大盅，送服西药阿斯匹林瓦许，周身得
汗，小便必然通利，而太阳之表里俱清矣。
以上所论述的伤寒太阳篇中的各方，虽然各不相同，但大抵都是治疗太阳经在表之病的方剂。至于治疗太阳腑病（膀胱及下焦病变）的方子原本不多，而治疗太阳腑病中最严重的情况，则是桃核承气汤。现在让我们进一步详细讨论它。
《伤寒论》原文说：太阳病（太阳经受邪所致的病证）未解，热邪结聚于膀胱，患者出现神志失常、似狂非狂的症状，如果瘀血能自行排出，病就会痊愈。如果表证仍未解除，尚不可使用攻下法，应当先解除表证。待表证解除后，如果仅剩下少腹（小腹部）急迫结痛的症状，才可以采用攻下法，适宜使用桃核承气汤。
【桃核承气汤方】桃仁五十个，去皮和尖；桂枝二两，去皮；大黄四两，去皮；芒硝二两；甘草二两，炙制。
以上五味药，用水七升，煮取二升半的药液，滤去药渣，加入芒硝，再次放在火上微沸，然后熄火。在饭前温服五合（约100毫升），每日服用三次，服药后应当会有轻微的腹泻。
此证是由于外感的热邪，沿着三焦脂膜下降，结聚于膀胱。膀胱上方与胞室（子宫或盆腔生殖器官）之间的脂膜相连，热邪向上蒸腾，导致胞室也蕴积了实热血瘀且运行不畅。而且热邪沿任脉上窜，扰乱心神（主宰精神意识的脏腑功能），所以患者会出现似狂的症状。
然而，病机的变化无穷无尽。如果胞室中的蓄血极多而自行排出，热邪即可随着血液一起下行，因此疾病可以痊愈。如果蓄血不能自行排出，且有欲下不下之势，这就非要用攻下法使其排出不可。只是因为外表证候尚未解除，或者因为误用下法后外感的热邪重新内陷，所以又适宜先解除外表证候，然后才能进行攻下治疗。
大黄：味苦、气香、性凉，原本就能开泄气机、破除瘀血，属于攻下药。但是如果没有专门入血分的药物来引导它，那么它破血的力量就不专一。方中使用桃仁，就是利用它能引导大黄的力量专门进入血分以破除瘀血的作用。徐灵胎说：桃花得三月春和之气而生，花色鲜明似血，所以凡是血郁、血结的疾病，不能自我调和畅达的，桃仁能进入其中调和消散。然而它生血的功效少，而去瘀的功效多的原因是什么呢？大概是因为桃核本身不属于血类，所以不能有所补益。如果瘀血都是败坏之血，没有生气就不能流通，桃子的生气在于桃仁，且其味苦又能开泄，所以能驱逐旧瘀而不损伤新血。至于方中又使用桂枝，也是因为它善于引导诸药进入血分，并且能引诸药上行以清除上焦血分之热，这样心神自然安宁，似狂的症状就可以痊愈了。
特别需要注意的是，使用桃核承气汤时，必须仔细斟酌。如果患者平日少腹经常感觉胀满，到了此时因外感的激发，而胀满更加严重，应当防备其素有瘀血。如果误用桃核承气汤攻下，那么排出的必定是紫色成块的死血，患者在排出这些血之后，十个人中难得救活一二。如果在临证时不得已必须使用桃核承气汤，必须向病人家属说明此事，以免产生误会。
热结膀胱的证候，不一定都会累及胞室蓄血。有的人患太阳病十多天未解，午前症状稍轻，午后则肢体酸懒、头目昏沉、身体似有灼热感、反而畏寒凉、舌苔纯白、小便赤涩，这只是热结膀胱而胞室并没有蓄血。这种情况应当用经府双解（既解表又清里）的方剂治疗，适宜用鲜白茅根切细二两，滑石一两，共同煮五六沸，取澄清的一大盅汤，送服西药阿斯匹林少许，周身出汗，小便必然通利，这样太阳经的表和里就都清净了。
The various formulas discussed above in the Taiyang chapter of Shanghan Lun, although different from one another, are generally used to treat diseases of the Taiyang channel (Taiyang Channel Disease) located on the exterior. As for treating diseases of the Taiyang fu-organ (Bladder and Lower Jiao pathology), there were originally few formulas; however, for the most severe cases of Taiyang fu-organ disease, Taohé Chengqi Tang (Peach Pit Decoction to Direct Downward) is indicated. Let us further discuss this in detail.
The original text of Shanghan Lun states: When Taiyang disease (Taiyang Channel Disease) does not resolve, heat becomes bound in the Bladder, and the person exhibits a manic-like state. If blood discharges spontaneously, the condition will heal. If the exterior syndrome has not yet resolved, attack methods should not be used yet; instead, the exterior should first be resolved. Once the exterior is resolved, if only urgency and binding in the lower abdomen remain, then an attack method can be used, and Taohé Chengqi Tang (Peach Pit Decoction to Direct Downward) is appropriate.
[Formula of Taohé Chengqi Tang] Tao Ren (Persicae Semen, 桃仁) fifty kernels, skin and tips removed; Guizhi (Cinnamomi Ramulus, 桂枝) two liang, skin removed; Dahuang (Rhei Radix et Rhizoma, 大黄) four liang, skin removed; Mangxiao (Natrii Sulfas, 芒硝) two liang; Gancao (Glycyrrhizae Radix et Rhizoma, 甘草) two liang, honey-fried.
Take these five herbs, boil them in seven sheng of water until two and a half sheng remains. Strain out the dregs, add Mangxiao (Natrii Sulfas, 芒硝), boil again briefly over fire, then remove from heat. Take five he (approx. 100 ml) warm before meals, three times a day. A mild purgation is expected.
This syndrome results from exogenous heat descending along the membranes of the Sanjiao (Triple Burner) and binding in the Bladder. The Bladder is connected via membranes to the Baozhong (Uterus/Pelvic Cavity). Heat steams upward, causing the Baozhong to accumulate excess heat and stagnant blood that fails to circulate. Furthermore, heat climbs along the Renmai (Conception Vessel), disturbing the Shen (Spirit/Mind), which causes the manic-like symptoms.
However, the pathogenesis is infinitely variable. If the stagnant blood in the Baozhong accumulates excessively and discharges spontaneously, the heat will descend with the blood, and the disease may heal. If the blood cannot discharge spontaneously and there is a tendency to discharge but fails to do so, it must be treated with purgation to force it downward. Because the exterior syndrome has not resolved, or because exogenous heat has re-deepened internally due to prior inappropriate purgation, it is necessary to first resolve the exterior before proceeding with internal purgation.
Dahuang (Rhei Radix et Rhizoma, 大黄): Bitter in taste, fragrant in aroma, cool in nature. It naturally opens qi and breaks blood stasis, belonging to purgative herbs. However, without specific herbs entering the blood level to guide it, its blood-breaking power is not focused. In this formula, Tao Ren (Persicae Semen, 桃仁) is used to guide the power of Dahuang specifically into the blood level to break stasis. Xu Lingtai stated: Peach blossoms grow in the harmonious qi of March, and their bright red color resembles blood. Therefore, for conditions of blood stagnation and binding that cannot self-regulate and flow freely, Tao Ren (Persicae Semen, 桃仁) can enter and harmonize/disperse them. Why is its ability to generate blood slight, while its ability to remove stasis significant? This is because the peach pit itself is not of the blood category, so it cannot provide tonification. Stagnant blood is ruined blood; without vital qi, it cannot circulate. The vital qi of the peach lies in the kernel, and its bitter taste allows for opening and draining, thus enabling it to expel old stasis without damaging new blood. Regarding the use of Guizhi (Cinnamomi Ramulus, 桂枝) in the formula, it is also because it excels at guiding other herbs into the blood level and directing them upward to clear heat in the upper jiao blood level. Thus, the Shen (Spirit/Mind) calms naturally, and the manic-like state heals.
Particularly, when using Taohé Chengqi Tang (Peach Pit Decoction to Direct Downward), careful consideration is required. If the patient habitually feels distension in the lower abdomen, and this distension worsens upon stimulation by exogenous pathogens, one must suspect pre-existing blood stasis. If Taohé Chengqi Tang (Peach Pit Decoction to Direct Downward) is mistakenly used to purge, the discharged material will certainly be purple, clotted dead blood. After such discharge, fewer than one or two out of ten patients may survive. If clinical circumstances necessitate the use of Taohé Chengqi Tang (Peach Pit Decoction to Direct Downward), this risk must be explained to the family to avoid misunderstanding.
Heat binding in the Bladder does not necessarily involve blood stasis in the Baozhong (Uterus/Pelvic Cavity). Some patients suffer from Taiyang disease for more than ten days without resolution. Symptoms are slightly lighter in the morning but include limb soreness and lethargy, heavy and dizzy head, sensation of burning heat in the body, aversion to cold, pure white tongue coating, and dark, difficult urination in the afternoon. This indicates heat binding in the Bladder without blood stasis in the Baozhong. This should be treated with a formula that resolves both the exterior and interior (Jing-Fu Dual Resolution). It is appropriate to use fresh Baimaogen (Imperatae Rhizoma, 白茅根) cut finely, two liang, and Huashi (Talcum, 滑石) one liang, boiled together for five or six boils to obtain a large cup of clear decoction. This should be taken with a small dose of Aspirin. Profuse sweating throughout the body will ensue, urination will become smooth, and both the exterior and interior of the Taiyang channel will be cleared.