You may as well find out what you're up to.
Xanax and Zoloft win. (Zoloft went generic in 2006. Current reduction in cost: zero.)
But, a little perspective:
Percocet is prescribed 3 times more than Xanax. Lipitor twice as often. Of course, the cost of percocet and Xanax are negligible relative to Lipitor.
Note also that the majority of "most prescribed" are generics. So where does the money go? Take Lipitor, which retails $800/yr for 10mg, $1300/yr for 20mg. Generic lovastatin 20mg costs $450. For that savings, you can slap on a Toprol XL 50mg (branded!) and a metformin, for good measure.
So wait a second, should we force all generics? No. Some don't have generics. So how do you reduce costs? Price caps? Useless. Then what? Not this fake, bureaucratic, pharmacy "formulary" with "negotiated" prices that are really extortion of Pharma by Medicaid and Medicare providers at patients' expense. Socialism isn't working in Venezuela, it isn't going to work here. To really reduce costs, you have to strike where it counts. And you're not going to like it.