This data is available here (file fjs10f18.cvs).
The Federal prison population was about 17 percent of the state prison population in 2011 (Appendix Table 1). In state prisons was a much smaller percent of the population there for drug offenses (about 17 percent in 2011). Combining state and federal prison populations together places the total prison population incarcerated for drug offenses at 21 percent.
For new admissions to the state prison population, drug offenses made up 28 percent. Federal drug offenders tend to punished relatively more severely than the average prisoner. The reverse is true for drug offenders in state prisons.