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.
In doses scarcely sufficient to make themselves felt in health, hyoscyamus appears to act as a nervous stimulant in disease, calming restlessness, and other forms of slight nervous disorder, and, in cases of morbid wakefulness, producing sleep indirectly by removing the cause which prevents it. In full medicinal doses, it often produces, along with some increase in the frequency of pulse and general warmth, or with no observable effect of the kind, an agreeable and diffusive feeling of comfort, followed perhaps by slight vertigo, or other uneasy sensations in the head, and after a time by an easy natural sleep. Sometimes, however, it occasions headache, and, instead of sound deep, gives rise to uneasy dreams, spectral illusions, or delirium. In not a few instances, nothing like sleep can be obtained from any ordinary dose; and, in such cases, some degree of sensorial or mental aberration is apt to occur, if the medicine is pushed. Dr. Pereira says that it is least apt to produce sleep in persons accustomed to the use of opium. A characteristic effect of it, as of other solanaceae, especially belladonna and stramonium, when the system is fully under their influence, is dilatation of the pupil. Besides these effects, it often occasions heat or irritation in the fauces, sometimes increases the perspiration or urine, and, in rare instances, has caused a pustular eruption upon the surface. Instead of constipating like opium, it either produces no effect on the bowels, or acts as a laxative; the latter result being not uncommon. In some persons, or in certain states of the system, it occasions general febrile heat and irritation. After the subsidence of its full direct effects, a state of greater or less depression occurs, which, when the quantity taken has been very large, may amount even to prostration.
Hyoscyamus has not unfrequently been swallowed in poisonous quantities. This has happened most frequently with the root, which has been taken by mistake for that of some other plant, as parsnep or chiccory. The effects are usually giddiness, more or less stupor, extreme dilatation of the pupils, disordered vision, spectral illusions, diminution or loss of the power of speech, accelerated pulse, delirium, sometimes violent and maniacal, sometimes low and muttering, often attended with laughter, tonic spasms, convulsions, coma, paralysis, and at length great prostration; with small and irregular pulse, difficult breathing, and coldness of the extremities. From this extreme condition, however, reaction generally takes place, and comparatively few cases terminate fatally. Yet death has occurred in several recorded instances. Sometimes, with these narcotic effects, symptoms of severe gastro-intestinal irritation are exhibited, as nausea, vomiting, abdominal pains, and purging. The administration of the medicine by enema, and its external application over the abdomen, have been known to produce severe symptoms, though never, I believe, fatal.
The operation of the poison usually continues for about twelve hours before abating spontaneously. The remedies are the same as those for opium; full vomiting being the most important. From the experiments of Dr. Garrod, it appears that animal charcoal is an efficient antidote to hyoscyamia, completely destroying its powers, even in small quantities. This, therefore, should be used, along with the other means employed, in the treatment of its poisonous effects. Of course it can exert no influence on the poison after absorption. (Med. Times and Gaz., Dec. 1857, p. 590).
The lower animals are affected very differently by the herb. Some, as horses, cows, sheep, goats, and hogs, eat it with impunity; while birds and dogs are affected like man. It is not impossible that injury may have accrued, particularly to children, from the use of the milk of cows and goats which have been feeding on henbane.
The effects of hyoscyamia have been carefully investigated by Prof. Schroff, of Vienna. In a moderate dose it produced dryness of the mouth and throat, dilatation of the pupils, diminution followed by increased frequency of pulse, vertigo, hebetude of mind, general feelings of languor, and finally quiet sleep. By larger doses these effects were produced in a greater degree. The dryness of throat was very great, there was difficulty of deglutition, the sense of taste and smell were impaired, headache came on, and a deep and quiet sleep closed the series. A solution of it dropped into the eye caused a dilatation of the pupil more rapidly, intensely, and for a longer time than any other agent. Given to rabbits in poisonous doses it produced deep sleep, followed by death, without any convulsive movements, or apparent delirium. It appeared to occasion inflammation of the lungs. This result is somewhat singular; as the same animals can eat the herb freely with impunity. (Wochenblatt der Gesellschaft der Aertze zu Wien, June 16,1855.)* Reisinger states culation than opium, and though, from this deficiency, it is of little use in supporting the system in certain conditions of debility where opium is highly valuable, it is more safely used in others, in which the anodyne and soporific properties of opium are wanted, but its stimulant property contraindicates it. Again, it does not constipate like opium, but is rather laxative, and cannot, therefore, be substituted for it in diarrhoea; but there are frequent occasions in which this dissimilarity gives it great advantages. Thirdly, it has no such effect in restraining the secretion of mucus, bile, and urine as opium has; and may on this account be sometimes preferably employed, where it is desirable rather to promote than to impede those secretions, as sometimes in the early stages of inflammation of the bronchial tubes, liver, and kidneys. Lastly, from individual idiosyncrasy, or peculiarity in disease, opium not unfrequently occasions so much nausea, headache, delirium, or other disagreeable effect, that it cannot be given, however strongly called for as an anodyne or soporific. In such cases, hyoscyamus may sometimes be substituted with great advantage.
* A solution of this difficulty will be found under belladonna, the peculiar alkaloid of which so closely resembles hyoscyamia, as to have led to the supposition that the two might be identical. It appears that the reason why certain animals can feed with impunity on the leaves of the solanacese is that, in consequence of the mass of matter in their stomachs undergoing digestion, the proportion of the poisonous principle absorbed, within a given time, is insufficient to cause a poisoned state that a single drop of an aqueous solution containing one part of it to ten of water, introduced into the eye caused dilatation of the pupil without irritation of the conjunctiva.
Though it would be difficult to prove that hyoscya-nuis operates upon the system through absorption, analogy leads almost necessarily to this conclusion. Its local action is that of a very moderate irritant, as shown by its occasional effects on the stomach, and its not unfrequent action upon the bowels. As a direct circulatory stimulant it is very feeble, being, in this respect, greatly inferior to opium; and, in many instances, the pulse is not affected, at least in frequency. The depression of the circulation which attends its full narcotic action is a secondary result, depending probably on the condition of the nervous centres. Its influence upon the cerebral centres is, I have no doubt, essentially stimulant; sleep resulting from a mild congestive action upon them, while, in a higher degree of the same operation, delirious excitement is produced, and, when the centres are quite overwhelmed, coma. The effect upon the pupil may be considered as a kind of sleep of the nervous centre, which causes contraction of the iris; or it may result from an excitant influence upon the sympathetic centres, producing a strong contraction of the dilating fibres.