Abbott Laboratories Inc. said Thursday it was halting sales of a 30-year-old attention deficit drug that a consumer group complained was too dangerous to stay on the market.

Abbott decided to discontinue the drug, Cylert, because of declining sales, Abbott spokeswoman Melissa Brotz said. The drug’s sales this year will be less than $1 million, she said.

Brotz declined to comment on charges made earlier Thursday from consumer group Public Citizen that the drug had caused 21 cases of liver failure, including 13 that were fatal or required transplants.

“We’re in the process of discontinuing it ... but that’s because of declining usage and sales and because there are generics available,” Brotz said.

Generic companies sell copycat versions of the drug under the name pemoline.

Public Citizen asked the U.S. Food and Drug Administration on Thursday to ban Cylert and its generic competitors immediately. Generic companies can still sell their versions even after Abbott pulls the medicine, unless the FDA determines the drug was withdrawn for safety reasons.

A petition from Public Citizen said Britain and Canada already had pulled the drug off the market, while the FDA opted to strengthen warnings twice and allow sales to continue.

The warnings failed to increase doctors’ monitoring of liver function in patients treated with pemoline, which offers no benefit over other therapies, the group said.

“In light of this evidence of unique liver toxicity without evidence of unique therapeutic benefit, we contend that the only responsible course of action is to remove this dangerous drug from the market,” Public Citizen said.

Cylert is a stimulant that was approved to treat attention deficit hyperactivity disorder, or ADHD, in 1975. Last year, about 117,000 prescriptions for the drug were filled in the United States, according to Public Citizen.

FDA spokeswoman Susan Cruzan said the agency would carefully review the petition, which also was signed by Dr. Fredric Solomon, a psychiatrist and ADHD specialist at the George Washington University School of Medicine.

Public Citizen has filed several petitions with the FDA seeking to have various drugs withdrawn.

Earlier this month, the FDA denied a petition from Public Citizen asking for a ban on AstraZeneca Plc’s cholesterol treatment Crestor.