Background: Russia, like many other places, is currently experiencing a proliferation of new psychoactive substances, many of which are psychostimulants. In St. Petersburg, these appear to be mostly congeners of cathinone. We sought to obtain qualitative data to better understand the impact on the health and behaviors of people who use drugs (PWUD) by recruiting individuals who reported recent use of psychostimulants. Methods: In-depth qualitative data on current drug use and its effects were collected through thirty interviews (n=30) and two focus groups (n=10: five male, five female). The interviews and focus groups also provided data on the social contexts of drug use including sexual behaviors and associated medical issues. Secondary data about online drug purchases were obtained from a source that accesses and analyzes darknet purchases. Qualitative data were initially coded using a priori codes developed on the basis of the interview guide, and then data were coded again inductively based on emergent findings from the data. Thematic analysis was carried out using OpenCode 4.0 qualitative data analysis software. Results: Thematic analysis of the interviews and focus groups identified distinct differences in behavior patterns between older, more experienced PWUD and a "new generation" of PWUD. Routes of initiation of drug use and sexual behaviors associated with drug use differed, but both groups reported high levels of unsafe injection and sexual behaviors. In interpreting the texts and purchasing data, we have attempted to anticipate how the drug use patterns can influence HIV transmission. Conclusions: The emergence of a new class of psychostimulant drugs presents new threats to the health of drug users and new opportunities to intervene to reduce those risks. The information obtained may assist HIV/AIDS prevention specialists and drug user support groups in their efforts to decrease unsafe drug use and sexual behaviors.