An unusual lawsuit claiming the Food and Drug Administration (FDA) overstepped its bounds by deciding that two generic drugs used to treat attention deficit hyperactivity disorder should no longer be substituted for Johnson & Johnson’s widely used Concerta has raised questions as to what extent the US regulator should be allowed to reclassify a generic drug, writes the Wall Street Journal’s pharmaceuticals blog Pharmalot.

The issue touched off by a unilateral FDA action is being raised within the agency following a lawsuit by one of the generics manufacturers, Mallincrkodt, and Pharmalot notes that the outcome could have implications for both generic drug makers and the FDA. After reviewing reports indicating that some patients were not getting the expected benefit, the FDA analyzed the generic products made by UK-headquartered Mallinckrodt and Brussels, Belgium-based UCB, finding that the drugs were not bioequivalent to those of Concerta or to an authorized version also made by J&J but sold by Actavis.

In November 2014, the FDA then changed the ratings for the two generics, which contain the same active ingredient as Concerta, so that they could no longer be automatically substituted at pharmacy counters. It gave the drugmakers six months to provide data showing bioequivalency or withdraw their products voluntarily.

Mallinckrodt challenged the agency’s authority to reclassify its generic, arguing that it failed to provide sufficient notice of its decision and violated the company’s constitutional rights. Moreover, it says the FDA acknowledged there are no safety or patent issues. With the deadline having passed at the end of May, the generics remain widely available. Both companies have told the blog that they are working with the US regulator.

Pharmalot says this is not the first time the FDA has reclassified generic drugs over equivalency, having reclassified some generic antidepressants in 2012. The Mallinckrodt challenge, however, is a first.