If the stats are to be believed:
-In 2008
18 pitchers in the league could throw over 100 mph and through the whole season they combined threw 196 pitches over 100+ mph
-In 2017
40 pitchers in the league could throw over 100 mph and through the whole season combined for 1,017 pitches over 100+ mph.
HGH comes to mind but they're clearly doping and getting away with it. What do you suppose they're using?
I saw a really interesting thing from Gorge St Pierre, a UFC fighter, about how athletes get around drug testing. I'll see if I can find it. The gist of it was there are drugs that are taken which are supposed to be 24 or 48 hour lifetime in the system and athletes plan around beig unavailable at these times for random drug testing ie;they will say they are travelling and just go hide for a day or so.
I remember when creatine became popular and it was a controversy as players began to shatter home run records left and right. Granted that's just the result of an increase in leverage and isn't related to steroids per say.