Source 出处 · Shanghan Lun · Doses are not given here: they are set by a licensed practitioner for the individual.
Safety. Chaihu Guizhi Tang is what you get when two of the most-used formulas in Shanghan Lun are put in the same pot: Xiao Chai Hu Tang for the half-exterior half-interior stage, and Gui Zhi Tang for the exterior. Neither is at full strength. The line that introduces it is short and precise — 伤寒六七日，发热，微恶寒，支节烦疼，微呕，心下支结，外证未去者. Fever with slight chills, painful limbs, a little vomiting, a sensation of something propped up under the heart, and the exterior pattern still present.
The item a modern reader is most likely to skim is 支节烦疼, aching in the limbs and joints, and it is the one that carries the most risk. Fever plus joint pain is a differential with a clock attached: septic arthritis destroys a joint within days and is drained within hours rather than observed; rheumatic fever, Lyme disease, parvovirus B19, rubella, hepatitis B prodrome, chikungunya and dengue, gout, adult-onset Still's disease, systemic lupus, reactive arthritis and infective endocarditis all present this way. Telling them apart requires the joint to be looked at, and where sepsis is possible, aspirated.
心下支结 — a propped, bound feeling below the heart — is the same epigastric territory that the Xiexin Tang family of formulas addresses, and the differential is the same one: reflux, functional dyspepsia, peptic ulcer with Helicobacter pylori, gastroparesis, pancreatic and biliary disease, coeliac disease, mucosal injury from non-steroidal anti-inflammatories or iron, and the standing fact that inferior wall ischaemia regularly presents as upper abdominal discomfort. 微呕, slight vomiting, belongs to that list too; with unintentional weight loss, persistent vomiting, or new symptoms beginning later in life, the plan changes.
This formula is also one of the better-known Kampo prescriptions in Japan, where saikokeishito has been used and studied in small clinical series, including in epilepsy and in febrile seizures. Those studies exist, and they are small; the effect is not established, and this entry makes no claim for it. If a study is worth citing, its size is worth citing too.
The safety notes are largely cumulative from the two parent formulas, which is part of the point — a combined formula carries both sets. Raw pinellia is a mucosal irritant through its calcium oxalate raphides and lectins and can swell the throat; only the prepared forms (法半夏, 姜半夏, 清半夏) are taken internally, and it is one half of the 十八反 incompatibility with aconite. 人参 is Panax ginseng, not Codonopsis (党参) and not American ginseng (西洋参), and carries case reports of reducing warfarin's effect, of hypoglycaemia, and of insomnia with palpitations. 甘草 brings the glycyrrhizin problem: pseudohyperaldosteronism with hypertension, hypokalaemia and oedema, dangerous when added to a diuretic or digoxin. 芍药 is ambiguous in the market between 白芍 and 赤芍, which are processed differently and are not interchangeable by name. 桂枝 carries cassia coumarin. 大枣 is dried fruit and therefore sugar. 柴胡 carries bupleurum's species problem and its interstitial pneumonia signal. 黄芩 carries the skullcap identification problem.
Two parent formulas in one bowl means two sets of cautions in one bowl, and that arithmetic is exactly what gets lost when a combination formula is described as gentle.
柴胡桂枝汤是《伤寒论》里两首最常用方的合方：小柴胡汤治半表半里，桂枝汤治表，两方各取一半相合，所以也有「两方并列」的说法。条文很短也很有分寸：伤寒六七日，发热、微恶寒、支节烦疼、微呕、心下支结、外证未去者。
最容易被今天读者一眼掠过的是「支节烦疼」，而它恰恰是风险最高的一项。**发热＋关节痛是一份带时钟的鉴别清单**：化脓性关节炎在数天内破坏关节，处置是数小时内引流而不是观察；风湿热、莱姆病、细小病毒 B19、风疹、乙肝前驱期、基孔肯雅热与登革热、痛风、成人 Still 病、系统性红斑狼疮、反应性关节炎、感染性心内膜炎都以这种方式起病。区分它们的办法是去看那个关节，怀疑化脓时是穿刺。
「心下支结」（心下如有物支撑结聚）与泻心汤类方是同一片区域，鉴别也是同一份：反流、功能性消化不良、消化性溃疡与幽门螺杆菌、胃轻瘫、胰胆疾病、乳糜泻、非甾体抗炎药或铁剂造成的黏膜损伤，以及下壁心肌缺血常表现为上腹不适。「微呕」也在这份清单里；一旦合并非自愿的体重下降、持续呕吐或晚发的新症状，处置路径就要变。
这首方在日本汉方里叫 saikokeishito，有用于癫痫与热性惊厥的小规模临床观察。研究是存在的，规模也确实是小的；**疗效未被证实**，本条目不为此作任何主张 —— 引用一项研究，就该连它的规模一起引用。
安全侧基本是两首母方之和，这本身就是要点 —— 合方承担两套警示。生半夏因草酸钙针晶与凝集素强烈刺激黏膜、可致咽部肿胀，内服只用炮制品（法半夏／姜半夏／清半夏），且它是十八反中与乌头类相对的一方。人参是 Panax ginseng，**不等于党参、也不等于西洋参**，有降低华法林效应的病例报告，另有低血糖、失眠与心悸的记载。甘草是甘草酸问题：假性醛固酮增多症（高血压、低钾、水肿），与利尿剂／地高辛叠加时危险。芍药在市售层面白芍与赤芍长期混淆，二者加工不同、不可按名互替。桂枝含桂皮香豆素。大枣是干果＝真实糖负荷。柴胡有品种混乱与间质性肺炎信号。黄芩有黄芩属误判问题。
两首母方同锅，就是两套警示同锅 —— 合方常被说成「平和」，而这层算术恰恰是被「平和」两个字盖掉的部分。