Sanofi failed to get the U.S Food and Drug Administration (FDA) approval for Lemtrada, a multiple sclerosis drug. This disapproval is expected to curtail the company goal of capturing a larger share in the market demand for the cure of sclerosis.

Lemtrada was first approved by the European Union September of this year and the drug became a part of the company’s acquisition of Genzyme in 2011. The said acquisition cost $20.1 billion.

FDA cited different reasons for the disapproval for the drug. One of which is that Sanofi’s Genzyme unit didn’t have the necessary proof about the benefits of the drugs. Sanofi reportedly did not perform enough “adequate and well-controlled studies” and the agency rules that Lemtrada has more side effects than benefits. Approval may be given as soon as the company presents more results from more studies focusing on the drugs.

However, Sanofi is set to file for an appeal, claiming that their product is well-made and could be a good treatment for sclerosis. Genzyme President David Meeker said that, “We strongly believe that the clinical development program, which was designed to demonstrate how Lemtrada compares against an active comparator as opposed to placebo, provides robust evidence of efficacy and a favorable benefit-risk profile.”

“This was a big blow for Sanofi, as Lemtrada would have provided a significant growth engine for the company as early as 2014,” said analyst at Bryan Garnier in Paris, Eric Le Berrigaud to Bloomberg. “The key question now is whether they will commit to financing new trials in a scenario in which they would be delayed by three years in entering a very crowded market in 2018 to 2019. I’m not very optimistic about the appeal of the FDA decision.”

The FDA’s disapproval will cause the delay of Lemtrada’s entry to the market and this might cause huge losses on Sanofi. Currently, the market for Lemtrada is being dominated by Teva Pharmaceutical Industries, Biogen Iden Inc, Tecfidera Copaxone, Biogen Idec Inc. (BIIB)’s, and Tysabri, Novartis AG’s (NOVN) Gilenya Avonex and Merck KGaA’s Rebif.