Can somebody explain this huge heroin epidemic in the US the last few years? Is it because of prescription pills in the 2000s so addicts had to switch to junk as a cheaper alternative (and the laws tightening on oxy & other prescription opiates)

I've looked at the statistics and there's been a huge increase in H addicts. This is actually one of my fields of study but I don't live in the US, so I'm curious.