It’s awfully hard to get unbiased estimates of illegal drug use, since you are asking people if they committed a crime. This 2014 paper, “The Changing Face of Heroin Use in the United States,” does what seems a creditable job*, and shows an apparent dramatic shift in the demographics of heroin addicts over time, as they write in their conclusion:
Conclusion: Our data show that the demographic composition of heroin users entering treatment has shifted over the last 50 years such that heroin use has changed from an inner-city, minority-centered problem to one that has a more widespread geographical distribution, involving primarily white men and women in their late 20s living outside of large urban areas.
This includes a shift in the racial composition of users:
As well as in the gender balance:
And an increasing portion of addicts who began using after receiving prescription opioids:
This corresponds with the CDC’s own numbers for more recent changes:
From the demand perspective, I’d be interested in if these heroin trends correspond as closely to SSI-D receipt as do prescription opioids. From the supply perspective, this Don Winslow article about heroin and the Mexican cartels is well worth reading, and suggests that changes in potency of the drugs are driving some of the growth in overdoses.
*They are conducting a present-day survey in clinics and treatment centers and comparing addict characteristics with when the addict states they started- there are certainly problems with this approach, but I don’t think they should mitigate the main trends.