气寒，味苦。有小毒。黑白二种。
《本草》云∶主下气，疗脚满水肿，除风毒，利小便。
海藏云∶以气药引之则入气；以大黄引之则入血。
张文懿云∶不可耽嗜，脱人元气。余初亦疑此药不可耽嗜，后见人有酒食、病痞，多服
食药，以导其气，及服藏用神芎丸，及犯牵牛等丸。如初服，即快；药过，再食，其病痞依
然。依前又服，其痞随药而效，药过后病复至。以至久服，则脱人元气而犹不知悔，戒之！
惟当益脾健胃，使元气生，而自能消腐水谷，其法无以加矣。
《心》云∶泻元气，去气中湿热。凡饮食劳倦，皆血受病。若以此药泻之，是血病泻气
，使气血俱虚损。所伤虽去，泻元气、损人，不知也。经所谓∶毋盛盛，毋虚虚，毋绝人长
命。此之谓也。用者戒之。白者亦同。
罗谦甫云∶牵牛，乃泻气之药，试取尝之，便得辛辣之味；久而嚼之，猛烈雄壮，渐渐
不绝，非辛而何！续注∶味苦寒，果安在哉。又曰∶牵牛感南方热火之化所生者也，血热泻
气，差误已甚。若病湿盛，湿气不得施化，致大小便不通，则宜用之耳。湿去，其气周流，
所谓五脏有邪，更相平也。经所谓一脏未平，以所胜平之。火能平金，而泻肺气者即此也。
然仲景治七种湿证，小便不利，无一药犯牵牛者，仲景岂不知牵牛能泻湿利小便？为湿病之
根在下焦，是血分中气病，不可用辛辣气药，泻上焦太阴之气故也。仲景尚不轻用如此，
世医一概而用之可乎？又曰∶牵牛辛烈，泻人元气，比诸辛药尤甚，以辛之雄烈故也。
气味寒，味苦。有小毒。分为黑、白两种。
《本草》记载：主治降气，治疗脚部胀满水肿，祛除风毒，通利小便。
海藏（张元素）说：用理气药作为引经药，则牵牛入气分；用大黄作为引经药，则牵牛入血分。
张文懿说：不可沉溺嗜好此药，否则会耗脱人的元气。我起初也怀疑此药不可沉溺嗜好，后来见到有人因饮酒进食、患有痞块病，大量服用食药来疏导其气，以及服用藏用神芎丸，或者触犯含有牵牛的丸剂。刚开始服用时，感觉舒畅；药力过后，再次进食，痞块病依然如故。依照前法再次服用，痞块随药物暂时见效，但药力过后疾病又复发。以至于长期服用，耗脱人的元气却仍不知悔改，对此必须警惕！只应当补益脾胃，使元气生成，从而自然能消化腐熟水谷，这种方法没有比这更好的了。
《心》（李东垣《医学发明》或相关著作，此处指代某医籍观点）说：泻损元气，去除气分中的湿热。凡是饮食不节和劳倦过度，都是血分受病。如果用此药来泻之，这是血病却泻气，导致气血都虚损。虽然损伤去除了，但这是在泻损元气、伤害人体，人们却不知道。经典所说：不要使实证更实，不要使虚证更虚，不要断绝人的寿命。说的就是这个道理。使用者要警惕。白牵牛的功效也是如此。
罗谦甫说：牵牛是泻气的药，试着取来品尝，就能得到辛辣的味道；长时间咀嚼，味道猛烈雄壮，渐渐不绝，难道不是辛味吗？续注说：味苦寒，哪里在呢？又说：牵牛是感受南方热火之气化而生成的，血热而泻气，错误已经很大了。如果病情湿邪盛重，湿气不能运化，导致大小便不通，才适宜使用它。湿气去除，气机周流，这就是所谓五脏有邪气，相互制约平衡。经典所说：一脏未平，用所胜之脏来平抑它。火能平金，而泻肺气者就是这种情况。然而张仲景治疗七种湿证，小便不利，没有一个方剂使用牵牛的，张仲景难道不知道牵牛能泻湿利小便吗？因为湿病的根源在下焦，属于血分中的气病，不可用辛辣的气药，去泻上焦太阴肺经之气的原因。张仲景尚且不轻易使用如此，世间的医生一概使用它，可以吗？又说：牵牛辛烈，泻人元气，比一般的辛药更为严重，是因为其辛味雄烈的缘故。
Nature is cold, taste is bitter. Slightly toxic. Divided into two types: black and white.
Bencao (Materia Medica) states: It governs descending Qi, treats fullness and edema of the feet, eliminates wind-toxicity, and promotes urination.
Haicang (Zhang Yuansu) said: When guided by Qi-regulating herbs, it enters the Qi level; when guided by Dahuang (Rhei Radix et Rhizoma), it enters the Blood level.
Zhang Wenyi said: One must not indulge in its use, as it will deplete the body's Yuan Qi (Original Qi). I initially also suspected that this herb should not be indulged in. Later, I observed people who, due to alcohol consumption, rich food intake, or suffering from Pi syndrome (abdominal masses), took large amounts of medicinal foods to guide their Qi, and consumed Cangyong Shenxiong Wan (Shenxiong Pill of Cangyong) or pills containing Qianni (Semen Kochiae). At first, they felt relieved; after the medicinal effect wore off, upon eating again, the Pi syndrome remained unchanged. Following the previous method to take it again, the Pi syndrome responded temporarily to the medicine, but after the effect wore off, the disease returned. Eventually, long-term use depleted the person's Yuan Qi without them realizing their mistake. This must be warned against! One should only tonify the Spleen and strengthen the Stomach, allowing Yuan Qi to generate, so that one can naturally digest and transform water and grain. There is no method superior to this.
Xin (referring to Li Dongyuan's work) stated: It drains Yuan Qi and removes damp-heat from the Qi level. Any condition caused by improper diet or fatigue involves pathology in the Blood. If this herb is used to drain it, it means draining Qi while the disease is in the Blood, causing both Qi and Blood to become deficient. Although the pathogenic factor is removed, it drains Yuan Qi and harms the person, a fact unknown to many. The Classics say: Do not reinforce excess; do not further weaken deficiency; do not cut short people's longevity. This refers to such cases. Users must beware. Bai Qian Niu (White Semen Kochiae) has similar effects.
Luo Qianfu said: Qianni is an herb that drains Qi. Try tasting it, and you will find a pungent flavor; chewing it for a long time reveals a fierce and vigorous nature, unceasingly intense. How could it not be Pungent? The continuation note says: Its taste is Bitter and Cold, where is that then? It also says: Qianni is generated by the transformation of Southern Fire-Heat. To say it clears Heat from Blood and drains Qi is a significant error. If the disease involves excessive Dampness, and Dampness cannot be transformed and distributed, leading to obstruction of urination and defecation, then it is appropriate to use it. Once Dampness is removed, Qi circulates freely. This is what is meant by "when the Five Zang organs have pathogens, they mutually regulate each other." The Classics say: If one Zang organ is imbalanced, use the element that overcomes it to balance it. Fire can overcome Metal, and draining Lung Qi is exactly this principle. However, Zhang Zhongjing, in treating seven types of Dampness syndromes with difficulty in urination, did not include any formula containing Qianni. Did Zhang Zhongjing not know that Qianni can drain Dampness and promote urination? It is because the root of Damp diseases lies in the Lower Jiao, which is a Qi disorder within the Blood level. Therefore, one should not use Pungent Qi-draining herbs to drain the Qi of the Upper Jiao Taiyin (Lung). If Zhang Zhongjing did not lightly use it, how can modern physicians use it indiscriminately? He also said: Qianni is Pungent and acrid, draining the person's Yuan Qi more severely than other Pungent herbs, due to its fierce and vigorous Pungency.