The physicians at drug and rehab facilities will do everything necessary to see that you come to no harm while you are detoxing. From my understanding, when doing rehab for drug abuse, once you are stabilized, the facility will want you to be off of all psychotropic medications, because many of these create dependencies of their own. Anti-anxiety medications fall into this category. As long as the doctors are following the standard of care for detoxification and rehabilitation, they are permitted to remove these medications. They would not, of course, remove medications for diabetes, heart disease, ect.
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