For years, the US pork industry has stood by the safety and efficacy of a controversial growth drug banned in nearly 200 countries. But now, thanks to Chinese regulations, the National Pork Board is quietly encouraging American pork producers to stop using it.

Ractopamine is a beta-agonist, a drug that changes animals’ metabolism so that they develop more muscle instead of fat. The result is a meat that is both leaner and, because muscle is heavier than fat, heavier. That translates into benefits for consumers looking to cut the fat in their diets, as well as producers, because hogs can get heavier on less food.

But ractopamine is far from a dream drug. “The drug has triggered more adverse reports in pigs than any other animal drug on the market,” Helena Bottemiller reported for the Food & Environment Reporting Network in 2012. Documented effects include “hyperactivity, trembling, broken limbs, inability to walk and death.” The FDA said the data didn’t establish cause and effect, and the National Pork Producers Council and National Pork Board have both said the drug is safe. But health and animal-welfare advocates have been sounding the alarm for years, noting that its impacts on human health are largely unknown and that the approval from Codex, the World Health Organization’s international food safety body, is based on a single study of six men, one of whom had to drop out because he experienced negative health effects.

The drug, approved by the US Food and Drug Administration in 1999, is banned in many countries, including the EU, Russia, and China, the number one pork-consuming country in the world.

In addition to its massive demand, China is an excellent trading partner for American pork producers because Chinese consumers like the byproducts Americans don’t want, such as feet, neckbones, ears, and stomachs. In 2014, the US exported $775 million of pork to Hong Kong/China, according to National Pork Producers Council.

Not all US pork is raised with ractopamine, but even producers using the drug had been able to sell meat to China for years through its “gray market.” However, that backdoor effectively ended last year under current President Xi Jinping. “He shut off that,” National Pork Board CEO Chris Hodges told Quartz.

By that time, the US pork industry was already having trouble in China. A few months earlier, Russia had stopped importing pork from the EU, forcing producers there to find another market. They did: China.

Now, the American pork industry is trying to regain share by reducing the use of the growth drug. Though Hodges says the National Pork Board isn’t taking a position on ractopamine, it is encouraging producers to reevaluate whether it’s worth it to their operations financially.

“What the Pork Board’s been doing is informing pork producers of the opportunity,” Hodges told Quartz.

In a room with Illinois pork producers earlier this month, Hodges stopped just short of telling producers to stop using the drug entirely. “I ask you to do the math in terms of what does ractopamine mean to your operation, what is the cost and what is the increase in value to you from your packer and from the industry as a whole,” he told the Illinois producers, industry publication AgriNews reported.

It’s unclear if producers are heeding the call. Neither Elanco, which manufactures the branded version of ractopamine, nor Zoetis, which makes a generic version, would comment to Quartz on whether sales of the drug had slipped.

Not everyone is convinced that cutting out ractopamine would solve the problem. “Were we to be 100% ractopamine free tomorrow, could we ship as much as we want to China? Unlikely,” Brett Stuart of market analysis firm Global AgriTrends, which counts Elanco as a client, told Quartz. “Bottom line of the China situation is that it’s very complicated. It’s much more complicated than just ractopamine.”

There are certainly no guarantees that removing ractopamine would open China back up to all the pork American producers wants to sell it, but Smithfield Foods, the world’s largest pork producer, may offer a glimpse at the opportunity. In 2013, just weeks after announcing that half of its pork would soon be ractopamine-free, it announced an impending takeover by China’s Shuanghui Group for $4.7 billion—making it the largest Chinese acquisition of an American company to date.