Linzess, the irritable-bowel-syndrome drug made by Ironwood Pharmaceuticals (IRWD) and Allergan (AGN) , will have to compete with a new pill from Synergy Pharmaceuticals (SGYP) .

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Late Thursday Synergy secured approval for a new constipation drug that will compete against a similar drug from Ironwood and Allergan, which has already been on the market for four years. The drug, Trulance, has a label that's very similar to Linzess, analysts say.

"We are thrilled with the approval of Trulance because it provides an additional, much-needed, new treatment option to help adults with chronic idiopathic constipation and their health care providers manage this condition," said Gary Jacob, CEO of the company, in a statement.

The company regained nearly all of the ground it lost Thursday in premarket trading Friday, up 1.1%, hitting $6.50 per share.

Meanwhile, Ironwood did not move ahead the of market's open. Allergan shares barely moved ahead of market's open Friday, falling eight cents to $214.50.

The one issue that could affect the uptake of Trulance is the reported side effect of diarrhea.

"We still expect the much lower diarrhea rate for plecanatide [Trulance] vs. Linzess to be instrumental in plecanatide commercial preference and success," analyst John Newman of Canaccord wrote in a note.

Newman predicted that the approval of Trulance 10 days before the FDA's deadline for ruling on the drug was a "positive endorsement" on the part of the FDA.

Newman maintains a buy rating on Synergy, despite FDA warnings about the drug that gave others pause.

JPMorgan analyst Anupam Rama wrote in a note that the firm believes Linzess will still be "more efficacious" than Trulance. This is thanks to the pain relief Linzess provides, on top of helping with constipation.

"Overall, the Trulance label is generally in line with our expectations, and we maintain that Linzess has key points of differentiation," Rama wrote. "A key difference is that the current CIC label does not account for pain symptoms, while Linzess' label does."

Rama has an overweight rating on Ironwood. 

Allergan acquired the rights to market Linzess abroad in December 2015, while Ironwood owns the rights to sell the drug in the U.S.

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