Recently California changed its laws to allow for a prior felony drug possession to be reduced to a misdemeanor. Any criminal defense attorney can do it for you, but it can be done without a lawyer, here’s how to do it:

How to apply Prop 47 (PC 1170.18) If Convicted, serving a sentence:

Defendant submits a petition to Court for recall of sentence. Upon receipt, Court determines if defendant satisfies criteria (i.e. convicted of specified offense and has no disqualifying prior convictions).
 If criteria is satisfied, then offense is reduced, and defendant is released with credit for time served, but is subject to parole under PC 3000.08 for one year unless the Court, in its discretion, waives the parole period.
 Court may deny reduction if its finds defendant would pose an “unreasonable risk of danger to public safety”. In reviewing, Court must consider:
o Defendant’s criminal history, including types of crimes, injuries to victims, length of prior prison commitments and remoteness of crimes.
o Defendant’s disciplinary record (or lack of) while incarcerated.
o Any other evidence the Court deems relevant in deciding if a reduction would result in an
unreasonable risk of danger to public safety.
 “Unreasonable risk of danger to public safety” is defined as an unreasonable risk that defendant will commit a new “super” strike.

If you have been Convicted, sentenced and time already served:

Defendant files a petition for reduction. Unless requested by defendant, no hearing is necessary. Upon receipt of the petition and verification that defendant satisfies the criteria the Court shall grant the reduction.
For pending cases it is expected the Court or DA will be reducing those immediately. For cases in which Formal Probation was granted the statute does not specifically address how to handle, but it seems logical that the intent would be the same as those who’ve been convicted and have served time, perhaps with the remaining period of probation converted to Conditional/Informal Probation.