Teva Pharmaceutical Industries may sell a generic form of Viagra starting in late 2017, Pfizer said on Tuesday. The announcement marks the end of protracted patent litigation between the two drugmakers.

Pfizer's U.S. patent on Viagra only lapses in 2020, including a six-month extension granted for having tested the medicine in young patients. But now, following its agreement with Pfizer, the Israeli drugmaker may launch its copycat version of the impotence drug years before other generic drugmakers.

Teva will be paying it royalties, Pfizer said in a statement, but did not disclose other financial terms of their accord.

Teva will be authorized to launch its U.S. generics by December 11, 2017, or earlier in certain circumstances.

The agreement with Pfizer is good news for Teva, which has been seeking new sources of profit due to the generic threat hanging over Copaxone, its flagship drug for multiple sclerosis – and one of the two proprietary drugs Teva has developed. (The other is Azilect, to treat Parkinson's.)

Copaxone has been responsible for a good half of Teva's profit. The drug company's stock has been pounded in anticipation of profit tapering off sharply in 2014.

Either, or

Last week Teva took the unusual step of providing two sets of forecasts for next year - one assuming the launch of at least two generic competitors to Copaxone in the United States on June 1, 2014, and the other assuming no U.S. generic competition in 2014.

Assuming Copaxone does face competition, Teva estimates it will earn $4.20 to $4.50 a share on an adjusted basis on revenue of $19.3 billion to $20.3 billion. Without competition, Teva projects earnings of $4.80-$5.10 a share on revenue of $19.8 billion to $20.8 billion.

Analysts forecast the company would earn $4.94 a share on revenue of $20 billion in 2014, according to Thomson Reuters I/B/E/S. In 2013, analysts project Teva will earn $4.99 per share on revenue of $20.1 billion.

Impotence is big business

Viagra was the first drug that actually worked in treating impotence. It was approved by U.S. regulators in 1998 and commands has annual sales of about $1.8 billion, including U.S. sales of $1.2 billion. But despite its patent protection, the blue pill began facing cheaper generics in Europe in June, including formulations sold by Teva.

Pfizer's basic U.S. patent on Viagra had been slated to lapse in 2012, which would have opened the floodgates to cheaper generics. But in 2011, during the legal battle with Teva - a federal judge in Norfolk, Virginia ruled that a secondary Pfizer patent covering the way that Viagra is used protects the oral drug from generic competition well into 2019.

Teva Pharmaceutical Industries stock started the day on the Tel Aviv Stock Exchange with a slight upward bounce, of 0.3% in preopening trade.