Abbott Laboratories’ attention deficit hyperactivity disorder drug, Cylert (pemoline), has been deemed too risky for the US market by the country’s drug regulator, the Food and Drug Administration. In a stark warning on its website, the agency said that the overall risk of potentially life-threatening liver failure outweighs the benefits of the drug, which was removed from the market by both Abbott and generics manufacturers back in May.

Cylert will remain available for prescription until supplies are depleted, but the FDA cautioned that it should only be used in patients who have failed to respond to other therapies and – if no benefit is observed within three weeks of completing dose titration – then treatment should be terminated.

Since Cylert’s launch in 1975, 15 cases of acute hepatic failure have been reported to the FDA, four to 17 times the rate expected in the general population. Of these, 12 patients died or underwent liver transplantation, and the FDA believes the risks associated with Cylert have been greatly underestimated because of the six-month latency period between treatment initiation and signs of liver injury.

However, Abbott has insisted it removed Cylert for commercial reasons only, telling Reuters: “Usage of pemoline products has declined significantly over the years.”