How close is Teva Pharmaceuticals (Nasdaq: TEVA) to launching a generic version of sanofi-aventis' (NYSE: SNY) Lovenox? That's literally the billion-dollar question.

As of the third quarter, Momenta Pharmaceuticals (Nasdaq: MNTA) and Novartis (NYSE: NVS) were on their way to registering more than a billion dollars in annual sales of generic Lovenox. A billion dollars for a generic! It helps that Lovenox was a multi-billion-dollar brand to begin with, and Momenta and Novartis didn't have any competition, so they could price the drug close to the brand-name price.

But an application by Teva and another by Amphastar Pharmaceuticals and Watson Pharmaceuticals (NYSE: WPI) were still pending at the Food and Drug Administration. The chance of another generic entering the market has created a wall of worry over Momenta's stock. A second generic is a triple blow to Momenta because it'll likely lower the market share, as well as the price the duo can fetch for their version, plus the launch of a competitor triggers a switch in Momenta's deal with Novartis from revenue sharing to a royalty from Novartis.

That brings us back to the question of how close Teva is to launching a generic version of Lovenox. Teva announced today that the FDA has a "short list of questions, which Teva intends to respond to in the near future." Momenta's shareholders took that to mean an approval is coming sooner rather than later and sent the shares down 20% today.

Maybe that's prudent, although without knowing exactly what the questions are, I think it's a little hard to know how easily it will be for Teva to answer the questions. Keep in mind that Lovenox is a complicated molecule. Teva's application has been under review by the FDA since 2003, and the FDA took five years to review Momenta's application. Momenta's scientists are experts in heparin -- the base molecule of Lovenox -- having helped the FDA sort out Baxter's (NYSE: BAX) heparin contamination issue. Momenta is even suing Teva, claiming that its method for analyzing and producing generic Lovenox is covered under patents issued to Momenta. Whether Teva has the same kind of experts to make the FDA feel confident that its generic is a match with the original remains to be seen.

Today's drop could be a good spot to buy the Motley Fool Rule Breakers recommendation if the launch of Teva's drug is delayed by the FDA or Momenta's patents. But those are two pretty big ifs, and shares won't reach their true potential until the billion-dollar question has a definitive answer.

Momenta made my list of Black Friday bargains. Here's the rest of the list.

Momenta Pharmaceuticals is a Motley Fool Rule Breakers recommendation. Novartis is a Motley Fool Global Gains choice. The Fool owns shares of Teva Pharmaceutical Industries. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.

Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.