As far as I have as always ascertained:
Formulations is basically empty but essential
Listings is the main database -- where you make changes to the medications and where AC goes to get the information
MedNames - The medications themselves complete with their form, i.e. capsules, tablets, etc.
MedsDetails -- MedNames plus strengths
Never fear about deleting the last two. You can delete them until the cows come home or even longer (until the script writer is fixed, couldn't resist) and they will just keep coming back. Kind of like Herpes. In fact, they are the two tables that MUST be deleted after a change if you want the change to be recognized.
I did a lot of trial and error with the medication database when I rebuilt the pediatric one. A lot of columns can be deleted. Even more than I have taken out. I will change that in Version 2.0. They can also be moved left to right or right to left. As far as the tables, these four and only these four are essential. I do not believe you can take out formulations even though it seems useless.
Brian most likely has a better answer than I, because he has devoted a great deal of time to the study of Microsoft Access while I am only reading six hours per day on SQL Server J/K.

But, in Access tables and databases are linked so that some tables are essential even though they seem to do nothing. All through the databases that you can access, there are tables that are empty.
Hope this helps.