This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
The effects of nux vomica, in small doses, are those of a bitter tonic, combined, when the quantity taken is sufficient to affect the system, with an influence on the nervous functions which is quite peculiar, and which, in its higher degrees, is so violent and dangerous as to give the medicine a place among the poisons From very small doses no effects are at first experienced; but, if repeated every six or eight hours, they will be found in the course of a day or two to increase the appetite, hasten the digestion, and act generally the part of a simple tonic; and, by carefully managing the dose, diminishing it, or suspending the medicine for a time when the slightest sign of its peculiar action upon the nervous system is evinced, the effects may be confined within the tonic limits. Often, however, there will be some increase of the urinary secretion, with more frequent micturition; and it is said that the medicine sometimes proves diaphoretic or laxative. In large doses, its operation upon the stomach becomes irritant, causing loss of appetite, epigastric uneasiness, cardialgia, and sometimes vomiting or purging.
When it is taken more largely than requisite for the tonic effect, an entirely new series of phenomena are developed. The first observable effect in this series is generally a feeling of stiffness or stricture in the muscles of the jaw, or at the back of the neck, or of weight or weakness with trembling of the limbs. Some resistance is apparently felt in opening the mouth widely; there is difficulty in taking a full inspiration; and after a time the feeling of stiffness may be experienced more or less ' elsewhere, upon any attempt at movement. Along with this symptom, there is an increased sensitiveness to external impressions, especially of the touch; so that a slight tap upon the skin will produce sudden and involuntary startings of the muscles; and twitchings or catching movements in the limbs are not unfrequently the first symptom which attracts particular notice. If, under these circumstances, the individual try to walk, there will be a sense of tottering or staggering, not from vertiginous feelings, but as if from want of power to regulate the action of the muscles. After some days there is often a feeling of formication, tingling, or itching on different parts of the surface, such as is commonly felt when the foot is said to be asleep. Sometimes this sensation is among the earliest phenomena; and it is occasionally so severe as to constitute the most prominent symptom. An eruption upon the skin has been noticed in some instances.
Under a somewhat more energetic influence of the medicine, the spasmodic startings become more frequent and severe; horripilations and shiverings, with darting sensations like electric shocks, are not unfrequently experienced; and the muscular stiffness increases and extends, so that the patient complains not only of rigidity of the limbs, but also of tightness about his throat, difficulty of deglutition, stricture of the chest and abdomen, and even involuntary erections of the penis; those muscles now becoming affected which belong but partially to the voluntary class.
With the powerful effects upon the nervous system above referred to, the circulation is little affected; the pulse being often slow and calm; and, when accelerated, as sometimes happens, it is so, in all probability, secondarily. The brain, too, is usually undisturbed; the mental functions being quite sound; though occasionally there may be temporary attacks of pain in the head, vertigo, tinnitus aurium, contraction or dilatation of the pupils, and sparkling or dimness of vision. A tendency to drowsiness or stupor has also been observed in some rare instances.*