Abstract： The theory of you gu wu yun （If there is enough reason， a toxic medicine can also be used without harm） originates from the Huang Di Nei Jing （The Yellow Emperor's Inner Classic），emphasizing that pregnant women suffering from severe diseases may be treated with drastic purgatives or toxic medicinals when syndrome differentiation is accurate. Qian Jin Fang（ Important Formulas Worth a Thousand Gold Pieces） exemplifies this theory in the management of pregnancy disorders. Using the classification criteria for medicinals contraindicated and cautiously used during pregnancy in Pharmacopoeia of the People's Republic of China（2025 Edition）， this study screened relevant prescriptions recorded in the Bei Ji Qian Jin Yao Fang （Important Formulas Worth a Thousand Gold Pieces for Emergency） and Qian Jin Yi Fang （Supplement to ′Important Formulas Worth a Thousand Gold Pieces'），analyzed the specific application of six Chinese herbal medicines （Cinnamomi Cortex， Rhei Radix et Rhizoma， Aurantii Fructus Immaturus， Aconiti Lateralis Radix Praeparata， Typhae Pollen， Phytolaccae Radix）， and summarized their medication rules from four perspectives：pathogenesis，compatibility，processing，and dosage，with reference to Xin Xiu Ben Cao （Newly Revised Materia Medica） of Tang Dynasty and other relevant literature. The findings indicated that Cinnamomi Cortex and Aconiti Lateralis Radix Praeparata were explicitly documented as "capable of inducing abortion" in the classics of materia medica in the Tang Dynasty. SUN Simiao employed processing methods such as stir-frying and steaming，combined with toxicity-mitigating compatibility and dosage control，to transform contraindicated medicinals into safe agents that both treat diseases and preserve the fetus. Although Rhei Radix et Rhizoma， Aurantii Fructus Immaturus， Typhae Pollen， and Phytolaccae Radix lack explicit pregnancy contraindications， fetal protection was nevertheless achieved through rational compatibility to support healthy qi， appropriate dosage form selection， and precise dosage control. Qian Jin Fang adheres to four principles in employing medicinals contraindicated and cautiously used during pregnancy：administering medicinals based on pathogenesis，medication only when there is enough reason； reducing toxicity through compatibility， supporting the healthy qi and preserving the fetus； attenuating medicinal properties by processing，reducing toxicity and enhancing efficacy；and discontinuing medication once the disease is resolved to a substantial extent. This medication system offers a literature foundation and reference for the rational use of medicinals contraindicated and cautiously used during pregnancy in modern clinical practice guided by accurate syndrome differentiation.