Investors dumped stock in Eli Lilly and Co. this morning after the company issued a long-term forecast that suggested its profit could tumble after patents expire on several of its bestselling drugs.

Lilly shares fell as much as 4.9 percent, to $34.76 each,  before recovering partially in late-morning trading.

The Indianapolis-based drugmaker expects to post profit of more than $3 billion each year from 2012 to 2014, according to Chief Financial Officer Derica Rice. Those are the years in which Lilly’s blockbusters Zyprexa, Cymbalta, Gemzar, Humalog and Evista could face competition from cheaper generic drugs.

But profit this year is on pace to exceed $4.5 billion and could approach $5 billion.

Lilly spokesman Phil Johnson emphasized that the $3 billion figure is a “minimum threshold.”

Lilly said it expects its earnings per share to grow in the double-digit range through 2011. The drugmaker expects to earn $4.65 to $4.85 per share in 2010, excluding the impact of health care reform and other items. On average, analysts expect income of $4.74 per share, according to a survey by Thomson Reuters.

Lilly said it would launch two new drugs each year beginning in 2013. The company has more than 60 molecules in clinical development, including 25 in mid- and late-stage development.

But since the blockbusters that will lose patent protection make up more than half of Lilly’s current revenue, investors and analysts do not think Lilly’s pipeline can make up the losses.

“Although Lilly has a growing mid-stage pipeline, these assets remain several years away from the market, leaving the company in the difficult position of needing to heavily invest in its next wave of product opportunities at a time of significant erosion,” Chris Schott, a JPMorgan Securities analyst, wrote to clients today, according to Bloomberg News.

In August, Lilly debuted blood thinner Effient in the United States, the company's first new product launch since 2005.

Lilly's fastest-growing product is Alimta, which saw its sales climb 47 percent in the third quarter. Lilly said Thursday it plans to pursue additional indications for the cancer drug, either as monotherapy, or in combination with other oncolytics.

Earlier this year, the Indianapolis company said it would cut annual costs by $1 billion by 2011 by trimming 5,500 workers (13.5 percent of its work force) and producing new drugs faster. Today, Lilly said its U.S. sales force would be 25 percent smaller in 2010 than it was at the beginning of 2009.

Lilly CEO John Lechleiter opened the investor meeting with a presentation meant to convince investors that Lilly’s high-risk strategy is the right one to take.

“We want you to leave this meeting sharing our confidence in our future prospect,” he said.