More precisely, there is a theory that nicotine becomes highly addictive in the presence of an MAOI which are naturally present in tobacco smoke, but not added to nicotine gum.

I was actually referring to inhalation vs ingestion; specifically how inhalation has a 10-20 second lag before the effects are noticeable whereas ingestion takes much longer - resulting in less behavioral reinforcement.

The MAOI theory is interesting, there are a lot of alkaloids in tobacco. Apparently nicotine uptake across alveoli membranes is very pH dependent - the ionic form won't cross the barrier. Cigarette smoke is cured at a high temp and has a low pH, pipe tobacco is cured at room temp and has a high pH. [0]

It seems that cigarettes are processed to specifically give a minimal dose per volume inhaled that quickly delivers nicotine as a way to maximize reinforcement behavior. I would be interesting to test the pH of commercial vaporization solutions.

[0]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2953858/

Super interesting. Thanks for taking the time to clarify.