This herb is a powerful poison that doesn't belong on the home medicine shelf.  Similar to nicotine, it has been used in over-the-counter preparations to help people stop smoking, however, there is no indication that it's useful in this area. 

Lobelia contains Lobeline and related alkaloids which act first by exciting and then depressing the central nervous system.  It can open the bronchioles if used in the right amount however, too much and it slows respiration and lowers the blood pressure drastically.   Different doses have different effects.  A half of a teaspoon of lobelia tincture may have a sedative effect but a whole teaspoon could cause you to vomit.

It is believed that Lobelia, administered by a professional, may be a nurturing and supportive tonic for the lungs, applicable to a wide variety of upper-respiratory ailments particularly helpful in the treatment of asthma and bronchitis.  Externally, lobelia may be useful in the treatment of arthritis, bruises, insect bites, poison ivy, ringworm and sprains.