I would suspect crack or meth usually mixed with opiods.
Dealers cut heroin with fentanyl or its vastly more potent analog, carfentanil. People go to heroin because it is cheaper than prescription opioids. Fentanyl and carfentanil are cheaper yet, because they can be made in garage labs, and the recipes are highly available. There is also a tendency to go for more and more potent stuff because addicts build up a tolerance for the weaker stuff.
And whenever there is a report that a batch of opioids is causing a higher than usual number of deaths from overdose, that is like an advertisement to addicts. They hear that and think, it must be some good stuff. And they seek it out.
I was about to ask if you think crack and meth are physically mixed with opioids? Or do you mean, the addict has a smorgasbord approach?