The U.S. Food and Drug Administration has reportedly allowed over a dozen potentially harmful antibiotics to be used in animal food, despite research studies claiming that these drugs are at "high risk of exposing humans to antibiotic-resistant bacteria through the food supply," an environmental advocacy group said in a report on Monday.

According to Reuters, a study released by the Natural Resources Defense Council, a non-governmental group, found that the FDA allowed 18 livestock drugs to stay on the market. Antibiotics are added to food and water given to healthy animals--like cattle, poultry and hogs--to help increase their weight.

Carmen Cordova, NRDC microbiologist and lead author of the study, said in a statement that the FDA were aware of the effects that the antibiotics had towards humans. She also called the FDA's failure to act on its own findings "irresponsible."

"The evidence is clear," Cordova said. "FDA continues to knowingly allow the use of drugs in animal feed that likely pose 'high risk' to human health. That's a breach of their responsibility and the public trust." 

FDA officials reviewed about 30 animal-feed additives between 2001 and 2010 and approved them to be used for "growth promotion of livestock and poultry." Despite several raised red flags, they were used as an effort to produce and sell more poultry. In a statement, the FDA noted that it reviewed approved penicillin and tetracycline products in 2001. The FDA sent out letters to companies asking for additional safety data.

"Based on its review of this and other information, the Agency chose to employ a strategy that would more broadly address the concerns about the production use of medically important antimicrobials in food-producing animals," the FDA said.

NRDC found that  that 18 of the 30 drugs posed a threat to humans, exposing them to antibiotic resistant bacteria through the food supply and affecting their health.

"This discovery is disturbing but not surprising given FDA's poor track record on dealing with this issue," Cordova said. "It's just more overwhelming evidence that FDA, in the face of a mounting antibiotic resistance health crisis, is turning a blind eye to industry's misuse of these miracle drugs."

Avinash Kar, an NRDC lawyer and one of the study's authors, said the new findings question whether new guidelines would be effective and stated that the FDA needs "to be doing better."

"The FDA's failure to act on its own findings about the 30 reviewed antibiotic feed additives is part of a larger pattern of delay and inaction in tackling livestock drug use that goes back four decades," Kar told Reuters.

Last fall, the Food and Drug Administration set new guidelines that call on global pharmaceutical companies to phase out the use of antibiotics in food production in order to uphold the effectiveness of certain drugs when used by humans.

Under those guidelines, food production will no longer be able to use antibiotics to make animals grow faster and stated that if farmers need to inject a sick animal with drugs, they will need to get a prescription from a veterinarian. The FDA asked companies to change their labels, ruling out medically-important antibiotics that refer to the use of animal growth.

"Resistant bacteria can contaminate the foods that come from those animals, and people who consume these foods can develop antibiotic-resistant infections," the CDC report stated. "The use of antibiotics for promoting growth is not necessary, and the practice should be phased out."