This is about as-yet Not-seriously-studied Gotchas.. not studied? Studied. some. but the $$ ran out because, nowhere in sight was
(say? instant gratification) for some nice, neat black/white Answer re the missing data.

SImilar propositions here, re ionizing radiation. a topic I happen to have some decades 'experiencing'.
http://forum.iwethey...iwt?postid=376910

In both cases, the Absence of a tidy summing-up is deemed a reasonable rubric for 'doing triage'==on to more pressing matters of the soluble/insoluble ilk.
In my case re (all sorts of radiation partaken-of, wittingly or not/by very many and in most populations):
I note that Today--as all along--even when you
Ask for a rendered-Dose--of the very technicians who are Supposed to speak physics? Frequently they Can't Tell You!

This means that: offering the patient that #, for his/her lifetime-accumulating Total Dose (if an Ept patient)
IS NOT EVEN on this multi-industries' RADAR.

[I have, today to respond to a questionnaire re. a recent X-ray/from the PR-folk at local hosp. Guess what my reply will be like?]
I KNOW my Σ RADs/REMs aka pre-'Sieverts' ... for complete Lab history.

Comparisons, then: I have observed this phenom since, well the Trinity Test? Willful ignorance is a windmill I will not tilt/waste no (more) time attempting to Educate-the-unwilling.

As to the 'brain changes' as a complex function of age, individual-brain-genetics, habits, duration of usage etc. of the (also-varying contents of quite more than THC)
One Hopes that research on [what can we Measure.. of these alleged brain Δs??] and like that.. shall persist, however likely funded ... at a pittance.

Peter is likely right as to the competition for some solution-like New Info on [n+1000] street-lamps to-look-under--on long lists.
The same may apply re cannabis: BOTH cases are about subtle (maybe usually) plus some prospects of severe Badness occurring--on a simply unknowable time-scale.
A severe 'there's the Rub', I wot.

We nitpickers serve our Purpose: but we may not expect our particular Nits to qualify for itch-scratching until the piles of heaped-dead-bodies become visible
(or odoriferous?)