id dosage the dosage and would much rather risk hurting my gi tract then my lungs with chemicals. ive had some fiendish tin foil days, my pipe used to be my one true love, but overall i wouldnt promote the use of such an administration method unless you have very good control over all variables and are aware of the potential pharmacokinetic changes accompanying such a method. im no chemist so i cant tell you exactly how exactly the molecule will be effected by too much heat, not without intense thinking and research anyway. therefore i cant tell you which products will result from the reactions caused by excess heat and how they in turn are processed once they hit our respiratory epithel. If the dosage becomes considerably higher, it is safe to assume that a fair amount of the substance somehow decomposes and I'd probably stay away. Tastes that don't resemble the substance's smell would make me careful as well.
I'm not sure whether I'm naive to the implications of all three listed variables in the *vaporizability* of a substance, but I don't see the melting nor the flash point having any large significance. Is a slow change to liquid state before the temperature passes the bp necessary for the stability of molecules? Anyway, cocaine has a pka of 8.2 so that's obviously no limitation to smoking either. my guess is that a correlation between stability of the weakest bonds within the molecule versus boiling point would be a major limitation to smoking it, but you'd best have a chemist comment on this, since these are all just half-educated guesses.
Thought about plugging it for rapid administration? It should be an option if you are looking for rapid onset without sticking needles into your body and in a worst case scenario of some irritation/pain you can still run to the crapper and get rid of the stuff. Dosage control is very easy this way, usually onset comes extremely fast and with a rise that is sometimes as steep as for IM administration. You would of course have to stick something up your arse.
Btw I don't think it is add, even if predictions can only be made with advanced theoretical considerations and advanced knowledge. :D