As a former cardio-pulmonary technician, who occasionally doubled as a respiratory therapy tech, I recall working at one hospital in Pennsylvania, at which the medical director of pulmonary medicine was a former Army assistant surgeon general. He used propylene glycol in aerosol treatments for older patients who had worked coal mines or steel mills in the area. When I asked him why he was using anti-freeze as medicine, he just shrugged and said it makes patients cough.
Distinct from polyethylene glycol, propylene glycol constitutes 89-90% of the formula for nicotine vaping cartridges. This 2017 study looks at the paucity of safety data. https://juniperpublishers.com/gjpps/pdf/GJPPS.MS.ID.555584.pdf
As a former cardio-pulmonary technician, who occasionally doubled as a respiratory therapy tech, I recall working at one hospital in Pennsylvania, at which the medical director of pulmonary medicine was a former Army assistant surgeon general. He used propylene glycol in aerosol treatments for older patients who had worked coal mines or steel mills in the area. When I asked him why he was using anti-freeze as medicine, he just shrugged and said it makes patients cough.