I feel bad for Tyreke, but reading about the NBA's drug program, it seems reasonably fair.
http://www.cbafaq.com/salarycap.htm#Q109"
Drugs of Abuse program: There are two stages to the Drugs of Abuse program. First-time patients enter Stage 1 of the program. A player who has already completed Stage 1 enters Stage 2. A player who has already completed Stage 2 is dismissed from the league. A player in the program can also advance one stage for disregarding his treatment program. Players continue to receive their salary in Stage 1. Players in Stage 2 are suspended during their inpatient care and for at least six months of their aftercare, until the medical director certifies that the player is ready to play. Players who fail to comply with their program are suspended in Stage 1, and dismissed from the league in Stage 2."
The penalty being dismissal with no intermediate suspension suggests that Tyreke wasn't cooperating with the NBA's drug treatment program. Maybe getting banned is the wake up call he needs... hope he has some people looking out for him.
From the same link, it seems unlikely that the drug offense is marijuana (only goes up to suspensions) or PEDs (which start with a 25 game suspension for a first offense).