Deaths from cannabis, LSD and similar drugs. Is this statistic calculated properly?

[Renald]

I am thinking about how deaths from drugs are calculated. We all know there are no deaths (or the amount is negligible) from some safe drugs like cannabis or LSD. But how are deaths calculated? I am almost sure there are deaths occurred from cardiac arrest or aneurysma rupture (or other acute cause) what happened during the intoxication with some kind of safe drug, but these deaths in official statistic are considered not death from drug usage, but death from some acute cause (heart, aneurysma etc.). If the death occurred during the effect of some drug, it surely had at least some effect, maybe not very significant, but non zero. What do you think, such a calculation is right?