A Skinny Label Is Worth a Few Hundred Million Dollars to Amarin

Amarin Corp. parlayed its only product, a synthetic version of a compound found in fish oils, into a heart medicine called Vascepa that analysts had projected could top $1 billion in U.S. sales by 2022.

That was until the drug’s main patents were canceled last year, ushering in generic competition that’s led Amarin’s stock to plunge more than 50%.

Now the Irish drugmaker, in a case that may have broad implications for the entire drug industry, is taking advantage of a controversial court ruling to try to get a generic competitor off the market. It involves what’s known as a ...