Eli Lilly (NYSE:LLY) is trying to perk up sales of Symbyax, a pill containing the active ingredients of its Zyprexa and Prozac. The drugmaker announced today that the Food and Drug Administration has expanded the label to include using Symbyax to treat patients with treatment-resistant depression, meaning they haven't been helped by at least two other drugs.

Being the last line of defense isn't usually a way to make big bucks. Drugmakers have to wait for patients to trickle through other medications and many patients will be sopped up by the other drugs. It's better used as a way to get your foot in the door, as Novartis (NYSE:NVS) is trying to do with Afinitor, its kidney cancer treatment for patients who have failed current treatments like Onyx Pharmaceuticals' (NASDAQ:ONXX) Nexevar and Pfizer's (NYSE:PFE) Sutent.

But Symbyax isn't your typical second-line treatment. Depression is a gloomy disease with up to 35% of patients failing to respond to two different treatments. That'll leave quite a few patients/customers still seeking treatment after trying drugs like Pfizer's Zoloft, GlaxoSmithKline's (NYSE:GSK) Paxil, or Forest Labs' (NYSE:FRX) Lexapro.

More importantly, Prozac is approved as a front-line treatment for depression, so the combination drug makes for an easy transition for doctors and their patients. Adding Zyprexa to a patient who is already taking Prozac may be an easier solution than changing medications all together.

Second-line treatments often aren't all they're cracked up to be, but for Eli Lilly, the research-and-development costs to expand Symbyax's label should be well worth the investment.

More Foolishness:

Pfizer is a Motley Fool Inside Value pick. Novartis is a Global Gains recommendation. GlaxoSmithKline is an Income Investor selection. Try any of our Foolish newsletters today, free for 30 days. We're not blue about the economy, and you don't have to be, either. 

Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool's disclosure policy hasn't felt this cheerful since the beginning of winter.