(Reuters) - Mylan NV’s long-awaited U.S. approval for its generic version of rival Teva’s blockbuster multiple sclerosis treatment Copaxone drove Mylan’s shares up around 18 percent on Wednesday while Teva shares plunged.

EpiPen auto-injection epinephrine pens manufactured by Mylan NV pharmaceutical company for use by severe allergy sufferers are seen in Washington, U.S. August 24, 2016. REUTERS/Jim Bourg/File Photo

The approval late on Tuesday by the U.S. Food and Drug Administration came earlier than both companies had expected. It was issued a day after the health regulator said it would introduce measures to speed to market generic versions of complex drugs like Copaxone to help address the rising cost of pharmaceuticals. [nL2N1MD10X]

Copaxone is the leading MS therapy worldwide as well as Teva’s best-selling drug, generating more than $4 billion in revenue for the Israeli drugmaker last year.

On Wednesday, Teva’s U.S.-listed shares sank 14 percent to $16.17, while Mylan’s shares rose $5.96 to $38.48.

Teva said that Mylan was launching the drug before resolving various patent appeals, meaning that Mylan may risk having to pay damages if Teva prevails.

The FDA approved two different doses of Mylan’s version of the drug, 20 mg and 40 mg. The 40 mg dosage accounted for more than 85 percent of Copaxone prescriptions in the second quarter.

Analysts called the approval a big win for Mylan and said it would help 2017 and 2018 earnings. Mylan filed its first application for a version of Copaxone in 2009.

Wells Fargo analyst David Maris said that optimistically the drug could add 13 cents a share to Mylan’s quarterly earnings going forward. That assumes Mylan captures a 40 percent share of the 40 mg dosage market at a 40 percent discount to Teva’s pricing.

Mylan had lowered its 2017 and 2018 earnings forecast in August, due in part to delays getting FDA approvals for key generics like its versions of Copaxone and asthma treatment Advair. At the time it said it did not expect any major product launches until 2018.

After the approval Mylan said it expected to start shipping its generic drug very soon. The FDA approval letter also said the company might be eligible for 180 days exclusivity on the drug, Mylan reported.

Momenta Pharmaceuticals and the Sandoz unit of Novartis already sell a generic version of 20 mg Copaxone and are developing a version of the 40 mg dosage.

But their difficulties in getting the higher-dose version approved had dampened expectations for Mylan before Tuesday. Momenta said the companies would still be able to launch during any exclusivity period if they receive approval.

JPMorgan analysts said Teva now faces full generic competition for Copaxone nine to 12 months earlier than expected. Teva has already been hurting due to weak generics prices in the United States and high debt.

Last month, Teva said it was looking to team up with other drugmakers to fund some of its development pipeline as it struggles with debt and expiring patents. The drugmaker’s specialty business has been losing ground since Copaxone ran out of patents.

In August, a U.S. House of Representatives committee contacted Teva, Novartis and five other makers of multiple sclerosis drugs as part of a drug pricing investigation, saying that some of the dozen drugs used to treat the progressive neurological disease appeared to have lockstep price increases.

The 2017 price for the 40 mg version of Copaxone is $80,000 per year and the 20 mg version is more than $90,000 after having been launched in 1996 at just over $8,000, the House committee said.

Shares of Biogen Inc, another maker of MS drugs, fell 1.4 percent to $315.99. Momenta shares fell 15 percent, or $2.65, to $14.85.