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.
I shall first treat of the effects of roasted coffee, and afterwards allude to the slight differences which exist between them and the effects of tea. Unroasted coffee, being almost never used, will not be considered.
In moderate quantities, coffee stimulates the stomach gently, and the nervous system decidedly, without much exciting the circulation, or producing any narcotic impression on the brain. These are the properties which characterize the nervous stimulants, and to this class, therefore, it properly belongs. It will be found to belong to the same class equally by its therapeutic effects. Upon those who use it habitually, its characteristic influence is not fully evinced; as it has either lost its power in great measure by repetition, or the secondary are so mingled with the primary effects, that the latter are not readily distinguishable. The following are the phenomena of its operation in a system not yet rendered insensible to it by habit.
The first effect of a moderate quantity is usually a warming cordial impression on the stomach, which is followed after a short time by an agreeable feeling of comfort or satisfaction, and an obvious exaltation of the imagination and intellectual faculties. The disposition to cheerful conversation, or to other exercise of the mental powers, is awakened along with this increase in their vigour. Every one accustomed to witness social coffee or tea-drinking, must have noticed the increased vivacity, the more rapid interchange of thought, the general buzz which spreads through the company after partaking of the beverage. The student finds himself capacitated for a clearer understanding, and more prompt appropriation of the subjects of his study; the writer, for a more vigorous exercise of his mental powers, a quicker and happier arrangement of his thoughts or fancies, and a much greater facility of expression. In my own person, I every day experience something of this effect from black tea. For hours after dinner, even a moderate and entirely temperate dinner, I am often unable to perform, at all to my own satisfaction, any intellectual task which may have devolved upon me. An immediate change is produced by the tea, and, after the closing meal of the day, I find myself possessed of my intellectual capabilities, whatever they may be, to their full extent. Along with this nervous excitement, there is a strong tendency to wakefulness produced; and, under the influence of the beverage, if taken rather late in the evening, one's labours may often be prolonged far into the night, without any sense of fatigue or disposition to sleep. One or two cups of strong coffee at bedtime not unfre-quently prevent sleep for the whole night; and persons who wish to watch prepare themselves often in this way. During all this time there is little acceleration of the pulse; and that which may be noticed is probably rather owing to the reaction of the excited nervous centres upon the heart, than the result of a direct influence upon the circulation. The state of exaltation subsides after many hours into a corresponding depression; and the self-indulgence is paid for the next day by feelings of gastric uneasiness, languor, and general malaise, which gradually wear off, or disappear under a repetition of the stimulant. It will be readily understood, therefore, that the habit of coffee-drinking is not on the whole healthful, unless carefully guarded as to extent, or counteracted by active physical exercise. I shall refer, directly, to the evils which are apt to result from the abuse of this luxury.
When coffee is taken in excess, it causes a feeling of oppression or anxiety in the epigastrium, with over-excitement of the nervous system, indicated frequently by vertigo, headache, palpitation, muscular tremors, and other symptoms of irritation of the nervous centres. But, even in the largest quantities, it never produces, so far as I have ever witnessed, intoxication or stupor, or any other of those peculiar effects on the brain, which characterize the cerebral stimulants or stimulating narcotics in full action.
The habitual use of coffee in excess is very apt to occasion a train of very disagreeable and annoying symptoms, which can only be got rid of by abandoning the habit. The constantly repeated over-excitement, followed by the as constant depression of the nervous functions, give rise at length to persistent irregularity; and the exhaustion of the excitability of the nervous centres by the strain to which they are subjected, ends in a deficiency of power, and a consequent insubordination of all the functions placed under their regulating influence. These effects are especially displayed in persons of susceptible nervous temperament, and those of sedentary habits. Some individuals appear to be almost insusceptible to influence of any kind from the ordinary use of coffee; and its effects, whether direct or indirect, may be greatly controlled by habits of steady and vigorous muscular exercise. Indigestion, habitual constipation, and torpor of the liver, are among the effects of its abuse exhibited in the digestive function; nervous headache, sick-headache, vertigo, various disorders of sight and hearing, neuralgic pains and an infinite diversity of disordered sensation, palpitations, muscular tremors, hysterical symptoms in women, hypochondriacal in men, are some of the consequences of the same abuse in the nervous system. As the blood-vessels are little excited directly by the stimulant, the vascular system is apt to suffer less than the nervous; and it is unusual to encounter, from the abuse of coffee, any of those inflammations, as of the stomach, liver, brain, etc., which are so apt to follow the use of the cerebral, or even the arterial stimulants in excess. Hence it happens that, unless the nervous disorder has been so long continued as to have at last brought about organic change, all that is necessary, in order to escape from the evils, is to abandon the use of coffee.
As illustrative of the above statements I will observe that, personally. being of a somewhat nervous temperament, I am unable to use coffee steadily without much suffering; and the same peculiarity belongs to most of my immediate family. For years I was troubled with frequently recurring nervous headache, which at times incapacitated me for the performance of any active duty. Scarcely a day passed without some uneasiness or deranged sensations in the head; such as roaring, buzzing, and singing in the ears, sounds as of pounding, or bell-ringing in the distance, swimming or vertiginous feelings, rnuscae volitantes, etc., etc.; and I never walked in the streets without the fear of a sudden attack of these symptoms, which, when they came, took away all mental energy. It occurred to me that a single cup of coffee, which I was in the habit of taking daily in the morning, and to which I had reduced myself from the necessity of escaping the dyspeptic sufferings which a more free use of it had occasioned, might be the cause of these distressing phenomena. I abandoned the habitual use of it, substituting black tea for coffee; and from two weeks after that time up to the present, a period of many years, I have been almost entirely free from the symptoms referred to.
I was once called to a female patient labouring under great gastric uneasiness, troublesome palpitations, distressing nervous disorder of various kinds, and extreme emaciation. I requested to see her tongue. It was covered with small black points, which she told me proceeded from some burnt coffee she had been chewing. I wished to know if she was in the habit of using coffee freely. "Yes, doctor," she replied, "I drink it at breakfast, dinner, and supper, and chew the grains between whiles." I requested her to leave off the use of it entirely. She did so, and quickly recovered her health. I have no doubt that a vast deal of disease in our country, especially among the women, who in general drink coffee habitually, and use too little exercise, originates in this cause ; and I have often been able to afford relief, in long standing cases of distress, by the simple measure recommended in the above case. I have dilated more largely on this point than may be deemed exactly in accordance with the general scope of this work; but I am desirous of impressing my views upon the profession, feeling confident that, if adopted, they will lead to beneficial results.