I have no idea how hard it is really but if it's true it is impossible, it is infuriating. People do research on substances that can kill a person with an invisible amount, blow up buildings, poison vast areas, all kinds of deadly things. But take a drug that any smart high-schooler can (and frequently does) access it - and it's impossible to research it! This is so infuriatingly insane.

"It is often difficult for researchers to gain access to the quantity, quality, and type of cannabis product necessary to address specific research questions on the health effects of cannabis use"

Being unable to research the effects of specific strains and how cannabis is administered beyond oral or combustible methods limits our understanding of the true net effect in reality. Different methods for vaporizing and strains with low THC - high CBD would likely show very little evidence for negative effects on the user. However, consistent tobacco rolled cannabis cigars for a recreational user may show loads of evidence for negative effects on health. Like eating unhealthy vs eating healthy. Not all food is created equal, just like cannabis and its methods of use.

As a computationalist, I believe it is perhaps when we have full understanding of the internal workings of the brain and how different components interact with each other to ensure the proper functioning of the mind in such a degree that it is possible to simulate one with behaviour indistinguishable from that of its biological counterpart then we can figure out exactly what effect THC can have on computations performed by the brain and how that would subsequently affect a person's health.

I always discover something new about the mind when I do marijuana. Or perhaps that is merely how it feels like.