Concerns over a drug called Ractopamine Hydrochloride used in feed for pigs has caused many countries to question the pork being exported from the US. The drug is used to keep pigs lean and encourage growth up until slaughter. Traces of the drug have been found in the pork meat. The European Union, China, and Taiwan have banned it's use citing concerns about the effects it may have on humans.
The article claims that this drug is fed to somewhere between 60 and 80 percent of pigs in the US and has led to more livestock sickness or death than any other drug in the industry. The drug has also affected cattle and Turkey negatively. The drug is in a class similar to drugs used to treat humans for things like asthma however this specific drug has not been approved for human use.