Animal rights and food safety groups are petitioning the U.S. Food and Drug Administration to immediately lower the allowed residue limits for ractopamine — a controversial drug used to boost growth and leanness in meat production — and to study the drug’s effects on human health and animal welfare.

The petition comes just days after the drug escalated trade tensions between the United States and Russia, which recently adopted a zero tolerance policy for ractopamine in imported meat, jeopardizing around $500 million in U.S. exports to the country.

“The continued use and abuse of ractopamine in our food supply needs to be put in check,” said Elisabeth Holmes, staff attorney at Center for Food Safety, which filed the 37-page petition with the Animal Legal Defense Fund.

The petition contends that the FDA needs to do a more thorough job of assessing the potential harmful effects of ractopamine, a beta-agonist that mimics stress hormones and increases the rate at which animals convert feed into muscle.

The agency approved ractopamine for pigs (sold as Paylean) in 1999, for cattle (sold as Optaflexx) in 2003 and for turkeys (sold as Topmax) in 2008. It is most widely used in pork production (estimated to be somewhere between 60 and 80 percent), but is also used by the beef industry. The drug is fed to animals in the last few weeks, right up until slaughter.

There is no mandatory withdrawal period for ractopamine, but when FDA approved the drug, it set safe maximum residue limits (MRLs) for ractopamine in meat products.

The U.S. Department of Agriculture’s Food Safety and Inspection Service does very limited testing for the drug, but the agency has never found levels that violate the established MRLs, according to the data posted online. A recent test conducted by Consumer Reports of 240 pork samples found that about one in five were positive for very low levels of the drug — under 5 parts per billion (ppb), which is well under the FDA’s established MRL of 50 ppb for pork.

The FDA’s MRL for beef is 30 ppb. Last summer, in an unusually contentious 69-67 vote, the Codex Alimentarius Commission adopted a 10 ppb MRL for both beef and pork.

Though ractopamine is approved as safe in more than two dozen countries, including Canada and Brazil, there is still sharp disagreement over the safety of the drug. The European Food Safety Authority has determined the science backing ractopamine is insufficient to determine what amount, if any, of the drug is safe for human consumption. China, Russia, and others have expressed similar worries and ban the drug from being used by their own meat producers. The European Union bans all growth promoters from meat production.

The petition filed this week asks the FDA to immediately review the Codex standards and meet them or set “more health- and welfare-based standards.”

The groups also want the agency to preform “comprehensive scientific studies needed to characterize the health, welfare, and behavioral risks posed by the use of ractopamine.”

“FDA must do its job of assessing risks, questioning health impacts, and providing better solutions for our food system.  American families and, potentially, the nation’s economy are at risk,” said Holmes in a statement Thursday.

While it was approved as safe by the FDA more than a decade ago, the petition claims the agency did not thoroughly review all of the potentially negative consequences of the drug. Animal welfare advocates are particularly concerned about the number of pigs that have reportedly had adverse reactions to the drug.

“More pigs have been adversely affected by ractopamine than by any other animal drug—over 160,000, by the FDA’s own calculations,” said Stephen Wells, executive director of the Animal Legal Defense Fund.  “The effects of ractopamine are cruel and completely avoidable.  At a time when consumers are increasingly demanding more humane treatment of animals slaughtered for the meat industry, the United States should be at the vanguard of strong animal protections, rather than behind the international curve.”

The high number of adverse reactions was first reported by the Food and Environment Reporting Network in an report: “The drug has triggered more adverse reports in pigs than any other animal drug on the market. Pigs suffered from hyperactivity, trembling, broken limbs, inability to walk and death, according to FDA reports released under a Freedom of Information Act request. The FDA, however, says such data do not establish that the drug caused these effects.”

The reports from producers led the FDA to add a warning label to Paylean in 2002, noting that the drug could increase the incidence of “downers.”

Elanco, the manufacturer of ractopamine, and the FDA did not respond for requests to comment on the petition.

Earlier this year, Elanco spokeswoman Collen Par Dekker said, “Our company takes adverse event reporting very seriously and is overly inclusive on the information we submit to ensure we’re meeting all requirements.” She said the label change resulted from an ongoing process of evaluating adverse effects of the drug, adding that an industry trend towards heavier pigs contributed to rising numbers of lame animals in this period.