> Set against a background of assumptions that heroin use is inevitably problematic, there is significant evidence of its controlled use. This paper attempts to draw together the literature on patterns of heroin use which avoid physical and psychological dependence.

https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1360-0443....

This paper is a great read on the topic. Some suggest more than 50% of heroin users are casual users.