Now for the technical part that my puny little brain can barely grasp. Hope I donít get you too confused. The constituents of a plant really are quite interesting, once you get into it. Though the whole plant is responsible for the action, not any single constituent, the constituents are the make up of the plant influencing its action. When we know which constituents are present and what their action is it helps us to understand the action of the whole plant in a clearer way.
Lobelia contains fourteen piperidine-type alkaloids with confusing tongue twister names. Lobeline, lobelanine, and lobelanidine are found in the greatest proportions. Lobelamine, norlobelanine, lelobanidine, norlelobanidine, norlobelanidine, lobinine, norlobeline (=isolobelanine), lelobanidine, lovinine, isolobinine, lobinanidine are present in lesser amounts. How would you like to rattle those names off one after the other? Iím afraid my tongue would get so tangled I wouldnít even be able to say lobelia anymore.
In addition to the alkaloids lobelia also contains a bitter glycoside (lobelacrin), chelidonic acid, lipids (fats), gum, resin, a pungent volatile oil (labelianin), chlorophyll, lignin, salts of lime and potassium, with ferric oxide. Another constituent of lobelia, beta-amyrin palmitate, has been studied for its antidepressant effects. In one study the in vivo actions of beta-amyrin palmitate on central nervous system activity were compared with those of two antidepressant drugs, mianserin and imipramine with positive results.
The pharmacological effects of lobelia are attributed primarily to the piperidine-type alkaloids, particularily lobeline. Lobeliaís alkaloids stimulate the vagus nerve which controls the stomach. Proctor was the first in 1838 to isolate the liquid alkaloid lobeline which scientists consider to be the active principle of lobelia. Lobeline is found in higher concentrations in the seeds than the rest of the plant.  The piperidine alkaloids are closely related to nicotine though less potent and have similar chemical effects on the peripheral and central nervous (CNS) systems.
Other research shows that the principle pharmacological activity of lobeline is not nicotine agonism. Rather, lobeline may affect CNS activity by altering the dopamine chemistry of the brain. Lobeline has been shown to be more potent than d-amphetamine in blocking dopamine uptake into synaptic vesicles. Lobeline induces reflex stimulation of the respiratory center by acting on the chemoreceptors of the glomus caroticus, producing stronger and deeper breathing. This helps to explain why lobelia is useful for respiratory complaints.
Isolobelanine also called norlobelanine has a balancing effect to lobeline, relaxing the respiratory and neuro-muscular system. Lobeline is a powerful respiratory stimulant, while isolobelanine is an emetic and respiratory relaxant. Can you see how the apparently paradoxical effects of stimulating and relaxing work so well together? Donít worry weíll get more into it when we discuss the medicinal qualities of lobelia.
 Hobbs, Medicinal Plant Constituents, introduction, p. 1-3.
 http://metagenics.com/resources/imc/OneMedicineProf/ProfHerbs/Lobeliaph.html; Hoffman, Lobelia inflata, http://www.healthy.net/asp/templates/article.asp?PageType=article&ID=1409; PDR for Herbal Medicines, 1999, p. 943; Stedman, Stedmanís Medical Dictionary, 26th edition, 1995, p. 992. Foster and Duke, Eastern/Central Medicinal Plants and Herbs, p. 207.
 Grieve, A Modern Herbal, p. 495; Mabey, The New Age Herbalist, p. 36.
 Christopher, Guide to Colon Health
 Grieve, A Modern Herbal, p. 495
 Grieve, A Modern Herbal, p. 495
 http:metagenics.com/resources/imc/OneMedicineProf/ProfHerbs/Lobelia.html; Karch, The Consumerís Guide to Herbal Medicine, ch. 6, Herbal Profiles, p. 127;
 http:metagenics.com/resources/imc/OneMedicineProf/ProfHerbs/Lobelia.html; Chevallier, The Encyclopedia of Medicinal Plants, Key Medicinal Plants, p. 108.
 http:altnature.com/gallery/Blue_Lobelia.htm; Hoffman, Lobelia, http://www.healthy.net/asp/templates/article.asp?PageType=article&ID=1409.