[card_zero]

Yeah, that thought struck me too, looking at the entire graph there can never be an absolute decrease. But then, which timescale is the salient one?

[robertlagrant]

In context it would be one that would show that marijuana legalisation was probably the cause.

[card_zero]

Indeed, it's probably not due to marijuana legalisation, unless the resulting decline had a four year lag period for some reason, which I won't attempt to argue.

[throwuxiytayq]

I’d be more surprised if the effect was immediate. Addiction takes years to develop, and years to recover from. I would also expect marijuana legalization to have more impact on (potential) future drug users than people already addicted to opioids.