I recommend reading the wiki page for
Meldonium. I found it interesting. Mostly just shows how complicated the whole doping issue is.
It's a drug developed in Eastern Europe (Latvia specifically), and mostly used there. Some claim it's on the banned substance list because of political reasons, and it does seem that the evidence for it being performance enhancing is maybe kinda shaky. Supposedly it's purpose for athletes is protecting the heart and muscles from damage during high intensity workouts. Which would explain a lot of athletes taking it.
I obviously couldn't tell what the truth is. But it wouldn't shock me if there was some truth to those claims.