Satisfaction guaranteed or we'll pay you to buy from our competitors! Sounds like a slick used-car salesman's gimmick, doesn't it?

Actually, it's Eli Lilly (NYSE:LLY) and Icos' (NASDAQ:ICOS) pitch for their drug Cialis. You can probably figure out what the companies mean by "satisfaction" just by knowing that the drug treats erectile dysfunction (ED). The "Cialis Promise" promotion offers a free trial of the drug for men who have never used it before and promises that participants not pleased with the results will receive a voucher for a competing product, presumably GlaxoSmithKline (NYSE:GSK) and Bayer's (NYSE:BAY) Levitra and/or Pfizer's (NYSE:PFE) Viagra.

The advertising for newer ED drugs, Cialis, and Levitra is ubiquitous, especially on television. I can't begin to count how many times I've seen a Cialis spot that asks, "Will you be ready?" -- a phrase inspiring enough for a Marines' recruiting ad. Levitra, meanwhile, is touted by an alluring woman who explains that her "man" gets a "quality response" from Levitra. It seems to me this script would work really well in a "Mad Libs" book.

Although the marketing is pretty aggressive, the money is well spent. The ED market is huge, and Pfizer, the first to enter the segment with its Viagra, is not about to surrender that medicine's leading position without a fight. In fact, the company recently initiated a loyalty program that furnishes certain customers with a free refill on Viagra after they fill six prescriptions.

As silly as this latest Lilly and Icos campaign seems, the two firms are only fighting fire with fire, and investors can rest assured that Cialis is up to the challenge. The medicine has important advantages over competing treatments, and the more folks that try the drug, the better its chances are of ultimately dominating this lucrative segment.

Fool contributor Brian Gorman is a freelance writer living in Chicago, Ill. He does not own shares of any companies mentioned here.