Is it possible to have certain prescription drugs that are covered under my Medicare Part D prescription drug plan when these same medications are actually excluded from the Medicare Part D program?

Yes.  For most people this question about the coverage of non-Medicare Part D medications seems to be not only confusing, but also a contradiction.

However, there are certain drugs that are, by law, excluded from the Medicare Part D prescription drug program. 

Such excluded prescription drugs include such medications as prescription vitamins or fertility drugs.

(Update: Please note that that as of 2013, Medicare Part D plans will include coverage of benzodiazepines and barbiturates.)

However, some Medicare Part D plans (or Medicare Advantage plans that offer prescription coverage, MA-PDs) have chosen to cover a certain number of these excluded drugs - outside of the Medicare Part D program.

In other words, certain drugs that are normally not part of a prescription drug program can be purchased using the Part D plan's cost-sharing discount or co-payments.  But the purchases of non-Part D or Bonus Drugs do not count toward your total drug spending as part of the Medicare Part D plan (also known as your true out of pocket cost or TrOOP).

What are some examples of Bonus Drugs?
Some plans offer coverage for (before 2013: Benzodiazepines such as Alprazolam and Lorazepam); Cosmetic drugs such has Vaniqa and Lustra; Erectile Dysfunction such as Viagra and Cialis; Infertility, Hair Growth and other desirable, yet excluded medications.

Bonus Drugs and the Donut Hole discount
Bonus Drugs are typically do not receive the Donut Hole discount and you can read more here:
Do I get a Donut Hole discount on my non-formulary drug purchases and will these costs count toward getting out of the Donut Hole?

Bonus drugs are usually offered through the Part D plan under a discount program.

Each Medicare Part D plan has a different policy on Bonus Drugs and may offer different Bonus Drugs  - or no Bonus Drugs at all.

If your not sure whether your non-Part D drugs are covered or discounted, contact your Medicare Part D plan's Member Services department and ask a Member Services representative about the plan's Bonus Drugs or whether Bonus Drugs can be added through the plan's Formulary Exception process.