A New York federal judge granted Amarin’s bid for “preliminary relief,” allowing the drugmaker to promote its Vascepa pill for off-label use without the threat of an FDA misbranded action, as long as its communications are truthful and nonmisleading.

Vascepa is approved by the FDA to treat patients with very high levels of triglycerides that have been linked to diabetes, kidney failure and pancreatic cancer. Amarin also wishes to market the pill to physicians for patients who have more moderately elevated levels of triglycerides in spite of already taking statins. While the FDA didn’t dispute that an approved ANCHOR study demonstrates that Vascepa significantly reduces triglyceride levels in patients with persistently high triglyceride levels, the agency refused to grant approval to Vascepa for such use.

After receiving a Complete Response letter from the FDA threatening Amarin with a misbranded action for promoting its fish oil drug to healthcare professionals for off-label use, the company filed a complaint claiming the regulator’s ban on off-label promotion, as it relates to truthful speech, is unconstitutional under the First Amendment.

In its complaint, Amarin said the FDA’s threat of a misbranded action was stopping it from telling doctors about the study, and sought relief so that it could promote its product for off-label use without the threat of criminal prosecution.

U.S. District Judge Paul Engelmayer in Manhattan granted Amarin’s bid for preliminary relief, in a decision that could open the door for pharma companies to more openly encourage doctors to try medications for uses the FDA hasn’t approved, Bloomberg suggests. While the decision is a preliminary injunction and not a final order, Engelmayer noted Amarin was likely to prevail.

Courts have considered First Amendment protection for off-label marketing before, Reuters reported, noting that in 2012, the Second Circuit overturned the conviction of a drug sales representative for off-label marketing — though it was still unclear whether that ruling shielded truthful off-label marketing in all cases. Engelmayer determined it did.

The 2012 appeals court decision, in United States v. Caronia, played a key role in Engelmayer’s decision, according to a New York Times article. The Second Circuit ruled “the government cannot prosecute pharmaceutical manufacturers and their representatives under the FDCA for speech promoting the lawful, off-label use of an FDA-approved drug.” What tipped the scale in Judge Engelmayer’s decision is that the statements Amarin wants to make are truthful, which the FDA largely acknowledged. Engelmayer thus determined the decision in the Caronia case prevents the regulator from taking any enforcement action based on statements about a drug that are true.

As predicted by the Times, the FDA will most likely appeal Engelmayer’s decision because it would eliminate an area in which the regulator has aggressively policed. The Times noted the FDA reached major criminal and civil settlements with GlaxoSmithKline ($3 billion), Abbott Laboratories ($1.5 billion), Merck ($950 million) and Amgen ($762 million) related to off-label promotions of their products over the past few years.