The US Supreme Court has ruled that states may not ban the sale to drugmakers of prescription drug data collected by pharmacies.

The justices' 6-3 decision, which strikes down legislation passed by the state of Vermont prohibiting the sale of such data, declared that "information is speech" and that "speech in aid of pharmaceutical marketing" is a form of expression protected by the Free Speech Clause of the First Amendment. 

By passing the law, Vermont "has burdened a form of protected expression that it found too persuasive. At the same time, the state has left unburdened those speakers whose messages are in accord with its own views. This the state cannot do," said Justice Anthony Kennedy, delivering the majority opinion.

"If pharmaceutical marketing affects treatment decisions it does so because doctors find it persuasive," the majority opinion went on, and added that: "the First Amendment directs us to be especially sceptical of regulations that seek to keep people in the dark for what the government perceives to be their own good."

However, the three dissenting justices described the Vermont statute as "a lawful government effort to regulate a commercial enterprise” and pointed out that it does in fact satisfy the First Amendment standard previously applied in Supreme Court rulings concerning commercial speech. Moreover, they said that the statute's prohibition on drugmakers using prescriber identifying information “works no more than modest First Amendment harm" and is justified by "the need to ensure unbiased sales presentations, prevent unnecessarily high drug costs and protect the privacy of prescribing physicians."

At best, the Court's majority decision "opens a Pandora's Box of First Amendment challenges to many ordinary regulatory practices that may only incidentally affect a commercial message," the dissenting justices warn.

Information provider IMS Health, one of the defendants in the case, welcomed the Court majority ruling as "clear and unmistakable." Laws such as the Vermont statute "violate the Constitution and do nothing to improve health care, reduce costs or protect privacy as proponents had claimed," said Harvey Ashman, senior vice president and general counsel at the firm.

"Transparency is vitally important to advancing healthcare. The availability of information on the prescribing practices of physicians enables communications about new medicines, best practices and safety updates. This information is essential to improved patient care and safety," he added.

The Court ruling was welcomed by the Pharmaceutical Research and Manufacturers of America (PhRMA) as "not only a victory for free speech but also a triumph for patients and future R&D by biopharmaceutical companies," but Vermont state Senator Patrick Leahy said the Court had "overturned a sensible Vermont law that sought to protect the privacy of the doctor-patient relationship."

"States like Vermont must be able to protect the privacy of sensitive information exchanged between a doctor and patient. This decision undermines that ability, and risks unduly influencing doctors in their future prescription choices," said Sen Leahy.

• The decision not only strikes down the Vermont law but could also lead to similar legislation in Maine and New Hampshire being declared unconstitutional or repealed. 35 other US states and the Justice Department backed Vermont's case.