There is evidence that Trigonella foenum-graecum L. (fenugreek), a traditional Chinese herb, and its components are beneficial in the prevention and treatment of diabetes and central nervous system disease. The pharmacological activities of trigonelline, a major alkaloid component of fenugreek, have been more thoroughly evaluated than fenugreek's other components, especially with regard to diabetes and central nervous system disease. Trigonelline has hypoglycemic, hypolipidemic, neuroprotective, antimigraine, sedative, memory-improving, antibacterial, antiviral, and anti-tumor activities, and it has been shown to reduce diabetic auditory neuropathy and platelet aggregation. It acts by affecting β cell regeneration, insulin secretion, activities of enzymes related to glucose metabolism, reactive oxygen species, axonal extension, and neuron excitability. However, further study of trigonelline's pharmacological activities and exact mechanism is warranted, along with application of this knowledge to its clinical usage. This review aims to give readers a survey of the pharmacological effects of trigonelline, especially in diabetes, diabetic complications and central nervous system disease. In addition, because of its pharmacological value and low toxicity, the reported adverse effects of trigonelline in experimental animal models and humans are briefly reviewed, and the pharmacokinetics of trigonelline are also discussed.