This section is from the book "Dental Medicine. A Manual Of Dental Materia Medica And Therapeutics", by Ferdinand J. S. Gorgas. Also available from Amazon: Dental Medicine.
Hypnotics and narcotics are medicinal substances which affect the cerebral and spinal functions by impairing or destroying nervous action, having first a stimulant effect, to which their therapeutic efficacy is in a great degree due. They allay cerebral or spinal irritability, relieve muscular spasm and also pain, and induce sleep. When administered to relieve pain, they are termed anodynes; to induce sleep, they are termed hypnotics or soporifics.
Narcotics fulfill two indications, namely: Exciting and depressing the nervous energy. For the first it is necessary to begin with small doses and repeat them frequently; for the second, a full dose must be given and not repeated for a considerable time. On account of the system becoming very soon habituated to the action of narcotics, when it is necessary to resort to their use for any length of time the amount must be constantly increased, in order to maintain the same impression. The difference between the susceptibility to their action when the body is in a morbid or healthy condition should not be overlooked. Hypnotics diminish the cerebral circulation by modifying vascular activity.
Under narcotics and hypnotics are classed such agents as opium and its different preparations, chloral, lactucarium, belladonna, stramonium, hyoscyamus, tobacco, lobelia, conium, aconite, cannabis indica, humulus, camphor, hydrocyanic acid, aconite, alcohol, chloroform, digitalis, ether, paraldehyde, potassium bromide, sulphonal, urethran, zinc bromide, etc., etc.