After you have successfully run the LIBNAME statement, you can test to see if your data set is already available using PROC CONTENTS:
proc contents data=drug_a.h188a;
run;
If your data is already there as a SAS data set, then you'll get a contents report and no errors in the SAS log. If your data was not in the library as a SAS data set, you'll get an error something like this:
ERROR: File DRUG_A.H188A.DATA does not exist.
If your data is already a SAS data set, you don't need to copy it to the WORK library to use it. You can use it right from the "drug_a" library without the need to make a copy. For example:
proc means data=drug_a.h188a;
class drug;
var age;
run;