American Materia Medica, Therapeutics and Pharmacognosy

As used by the mouth, prior to our knowledge of its peculiar action
hypodermically, it was determined that lobelia in toxic doses causes
extreme prostration, burning pain in the esophagus, rapid, feeble pulse,
fall of temperature, collapse, coma or convulsions and death from
respiratory failure. Moderate doses cause dizziness, nausea, vomiting,
headache and general tremors. In doses of twenty grains it is a prompt
emetic, but emesis is accompanied by excessive prostration, relaxation
and a feeble pulse. In small doses it causes increased expectoration and
diaphoresis. Like other narcotics, a small dose stimulates, while a large
dose depresses the nervous system.
Although usually classed among emetics, lobelia is a nerve sedative of
great power, and in this influence as an antispasmodic it is exceeded by
but few remedies.
Death has occurred in a very few cases from excessive doses of the
remedy, but toxic effects are not apparent where the medicinal dose is
prescribed. Where death has occurred, its influence as a nerve
depressant has been plainly shown in the profound, general muscular
relaxation, with greatly impaired muscular power, general trembling,
shallow respiration, cold, clammy skin, feeble and depressed heart
action. It acts like tobacco and physostigma upon the respiration, the
heart's action continuing after the respiration has ceased. Paralysis of the
respiratory nerves is its prominent influence.
The observations made of its physiological action when the remedy is
used hypodermically are, that so used, the direct local influence of the
agent upon the stomach is avoided and if the remedy is properly
prepared, emesis, violent vomiting, profound relaxation, with prostration
and depression, which were found present from that local influence are
all absent. A total of less than five per cent of the cases will show emesis
or even nausea.
Used in a medicinal dose, it softens the pulse, slows the respiration,
quiets the nervous system, and produces a freedom of the respiration and
circulation. One of our writers claims that he believes that the agent
introduced by the stomach acts upon the pneumogastric nerve, while,
when introduced hypodermically and absorbed, it acts more directly
upon the sympathetic nervous system.
Lobelia acts directly upon the regulating centers of the system; those of
heat, of the circulation, of nerve influences, both motor and sensory. It
Ellingwood’s American Materia Medica, Therapeutics and Pharmacognosy - Page 277