A drug that farmers have given to chickens for decades is being pulled off the market after federal scientists found a potentially carcinogenic form of arsenic in the livers of animals treated with the substance, officials announced Wednesday.

Alpharma, a subsidiary of Pfizer, is voluntarily suspending sales of the drug 3-Nitro, which has been given to chickens since the 1940s to protect them from a parasitic disease and help them gain weight, the Food and Drug Administration announced.

The action comes after an FDA study of 100 broiler chickens found a form of arsenic known as inorganic arsenic, which is a known carcinogen, at increased levels in the livers of birds treated with the drug compared to those that were not, the agency said.

During a briefing for reporters, David Goldman of the Agriculture Department and Bernadette Dunham of the FDA stressed that the levels of arsenic detected in the chickens were very low and do not pose a health risk to consumers.

As a result, there is no need to recall any chickens treated with 3-Nitro from the market or for consumers to avoid eating chicken while the drug is removed, the officials said. The decision to remove the drug was made to eliminate a source of exposure to the substance.

“Consumers can continue to eat chicken as 3-Nitro is recalled from the market,” Dunham said.

Alpharma will continue to sell the drug for 30 days to give farmers time to switch to other drugs, the FDA said.

The FDA approved 3-Nitro, also known as Roxarsone, in 1944 as the first new animal drug containing a form of arsenic known as “organic arsenic,” which is harmless and was thought to be excreted by the animals. While it is used in turkeys, chickens and pigs, farmers give it primarily to chickens to help control the parasitic disease coccidiosis, to promote weight gain and for “improved pigmentation,” the FDA said.

The agency conducted its study after research in recent years indicated that organic arsenic could be converted to the carcinogenic inorganic form.

Although organic arsenic is found in other animal drugs, there is no indication they pose a danger, the officials said.

In a statement, the National Chicken Council, an industry group, said that chicken remains safe to eat. “Chicken companies will continue to safeguard chicken flocks because healthy flocks are needed to produce healthful food for people. Consumers can continue to buy and eat chicken as they always have,” it said.