As the use of Chinese herbs in veterinary medicine increases it becomes more important to know what herbs are toxic and how to prepare and use herbs correctly to reduce the incidence of adverse effects. The herbs Aconite (Chuan Wu), Aconite (Cao Wu), Aconite (Fu Zi) and Aconite (Xue Shang Yi Zhi Hao) contain aconitine and may cause nervous system stimulation, then inhibition and death. The aristolochia herbs Guan Mu Tong, Ma Dou Ling, Qing Mu Xiang, Tian Xian Teng, Guang Fang Ji and Xi Xin contain aristolochic acid that can be nephrotoxic. The herb Ephedra (Ma Huang) contains ephedrine and pseudoephedrine that can cause cardiovascular disorders and death. The herbs Melia (Chuan Lian Zi), Pinellia (Ban Xia), Xanthium (Cang Er Zi), Dioscorea (Huang Yao Zi), Asarum (Xi Xin), and Tripterygium (Lei Gong Teng) can be hepatoxic. Gastrointestinal (GI) signs including GI bleeding may be associated with Sparganium (San Leng), Zedoaria (E Zhu), Sophora (Ku Shen), Rheum (Da Huang), Xanthium (Cang Er Zi), Cassia (Jue Ming Zi), Pharbitis (Qian Niu Zi), Croton (Ba Dou), Phytolacca (Shang Lu), Euphorbia (Gan Sui), Genkwa (Yuan Hua) and Brucea (Ya Dan Zi). Adverse reactions are due to the use of known toxic herbs, mistaken herbal substitutions, inappropriate use of herbs, processing mistakes, herb overdose, inappropriate herbal combinations, drug interactions with conventional pharmaceutical medications, individual patient sensitivity and misdiagnosis and mistreatment of the traditional Chinese veterinary medicine pattern diagnosis.