E.g. death due to X tends to depend greatly on what the policy is on autopsies and other checks, and whether or not there's any pressure on coroners to speculate about cause of death vs. just pronounce a generic reason.
In Norway for example, an autopsy only happens rarely unless there is a reason to expect foul play, mostly because it's seen as expensive and unnecessary. As a result, a lot of "natural causes" or "heart failure" can obscure more specific causes that will only be recorded if accompanied by e.g. police observations.
Then, even if you do tests, there's the question of how you record deaths where there are multiple possible causes. E.g. you might have heart failure possibly due to a combination of alcohol and other drugs. Depending on your reporting system you might put it down in any number of different ways.
Then on top of this, you have to consider what make people use, not just what potentially make people not use. It could be the differences in legal system, or just that other societal differences makes fewer people predisposed to want to use in the first place.
All of this basically makes it impossible to compare country to country and conclude that changes in a single area such as law enforcement makes a difference.
The reason we look to Portugal is not primarily because it looks good compared to other countries, but because it performs well compared to itself prior to decriminalisation, and because it was a recent change.
Really? That's interesting. In neighbouring Finland, an autopsy is standard practice whenever the medical cause(s) of death is not completely clear.
Anyway, it's a relevant point that you make about death being caused by multiple factors, and crediting the causes in statistics is a game that can be played.
Found that out when my dad died in 2000, and we asked for one - we didn't expect foul play but he'd struggled with alcohol problems in the past and for closure we wanted to understand if he'd gotten back into drinking and that might have been why he died (he had heart problems and were on drugs that would have made combining them with alcohol a likely cause).
The coroners office made it very clear that that since it was clear he died from his heart stopping and there was no immediate reasons to suspect that there were any external factors that'd make a difference to the primary reason of death and no suspicion of foul play, an autopsy was out of the question unless we were prepared to cover the full costs (which were fairly steep).
That he may or may not have taken his heart medicine or may or may not have combined it with alcohol was to them irrelevant as long as it didn't change the main cause and they had no reason to see the distinction as relevant.
If there was doubt about the major cause, such as e.g. if he'd had a head wound or something else that might have indicated another cause, it might have been different.
This might very well also vary from coroners office to coroners office in some countries depending on capacity. This was in Oslo, so would have been one of the busiest areas.
And among the worst offenders are the liberal states of Sweden, Norway, Denmark etc..
So - having extreme anti-drug laws combined with nationalist/patriotic crazy authoritarian government is the policy to go with?
I'm kidding .. but you see that it's hard to look at that chart and make out more than Apples to Oranges.
It's also worth pondering how Eastern Europe has a tiny fraction of the problem that West seems to have, except for Estonia, which seems of the charts. It really is a tricky graph.