It’s both actually. Obviously if you make drugs more rare, the price goes up. And when the price goes up, there will always be an amount of people that cannot pay it. The problem is that they’re then usually pushed to do something cheaper, but if the cheaper drugs are less likely to harm people, that can be a win.
Cutting supply isn’t everything, but it isn’t nothing. Part of the current problems are actually worse though because the worse drug is being added to a lot of other drugs that already have demand. So in this case it would help a lot more than usually because the dangerous substance isn’t necessarily what the addiction is for.