Fu Zi (Aconite) is a commonly used herb in traditional Chinese medicine (TCM) in China. It should be prescribed with caution. It is a challenging herb to correctly use without side effects, and cases of toxicity have been reported. Many TCM and traditional Chinese veterinary medicine (TCVM) practitioners in China have reported excellent therapeutic effects with Fu Zi (Aconite), but the human therapeutic dosage varies from 0.3-600 g/day, a 2000-fold variation. The dosages of most drugs in conventional medicine vary little and are primarily determined by body weight. Therefore, it is difficult to understand the variability in dosage and effects of Fu Zi (Aconite) from a conventional medicine paradigm. The variability of dosages and effects of Fu Zi (Aconite) and other Chinese herbal medicines and TCM patterns are non-linear and can be best understood from a Complexity Science perspective. Complexity Science is a non-linear mathematical model used to study the behavior of complex, dynamic and adaptive systems. According to Complexity Science, a complex system, such as human/animal, responds in a variety of non-linear ways. A small stimulation may cause a large reaction, while larger stimulation may only produce a small reaction or no reaction at all, depending on the specific situation. The variations in dosage, effects and toxicity of Fu Zi (Aconite) are closely related to the patient’s initial conditions (eg, interactions of biological clock, Constitution, Zang-fu organ interactions, underlying TCVM patterns) and can only be fully understood using a model like Complexity Science that considers these complex interactions.