Completely exclude medications even in a 3-tier plan?

If those medications use co-payment coupons to circumvent your benefit design then I suggest the answer is yes.

From RxObserver:

"PBM Express Scripts was recently in the news for announcing that its 2014 formulary would exclude from all coverage 48 prescription products.  Some 93% of the newly excluded products use copay coupons to get around plan design features intended to encourage plan beneficiaries to use less expensive, but equally effective prescription drugs. "