IIf my idenity was use for drug charges by someone else, how can I get these charges off my crimnal background?

The process of clearing up a criminal history report is somewhat similar to clearing up your credit report... tedious, but doable.  Your first step is to request a copy of your report.  You can do this in a couple of different ways.  You can purchase one online through the DPS website, or go to your local sheriff's office to request one.  You need the report so that you can see what, if anything, comes up on your record.  DPS maintains the central database for criminal history information in Texas.  So, if something does show up that is not your history, you will need to contact DPS and follow their procedures for disputing info on their report.  (This is similar to the dispute process you would use for your credit report).  Getting it off of your DPS-criminal record is just your first step.  DPS sells their data to private companies-- like the three major credit reporting companies.  After you get DPS to correct their records, you will want to go through a similar process with a private criminal background company-- get the report and then dispute the report.  You may have to dispute the info with a couple of different companies depending on how many companie the DPS has sold your information to.