Former Eddie's Farmhand Josh Flores has been suspended for 50 games following a positive test result for a drug of abuse.
Flores was released back in June, and his suspension will begin if he signs with another team.
Mitch Einertson was the last Astros prospect to be suspended for a drug of abuse, which the Biz of Baseball (linked) lists as:
4. Opiates (e.g., Heroin, Codeine, Morphine)
5. MDMA (“Ecstasy”)
6. GHB; and
7. Phencyclidine (“PCP”)