It was the largest increase because of the large drop in 2018 and small 2019 rise from that low point. Yes, I am saying that the 2020 rise was in line with expectations and any attempt to link it to lockdown will be weak. In five years they will be able to show the graph without years on it and most would guess 2018 as the lockdown year due to the anamoly.
In recent years? The adulteration of heroin with cheap fentanyl out of China made it much more dangerous for users because the dosage become much more uneven and this invited overdoses, while the crackdown on Oxy supplies over the past four or five years has shifted a lot of addicts away from a pharmaceutical-grade source of opioids and over to the previously mentioned dangerous heroin.