The US Food and Drug Administration (FDA) is increasingly paying attention to social media, and in particular Facebook, as companies use the social networking platform to market their products.

Six Warning Letters in Six Months

In at least six Warning Letters issued since October 2014, FDA has referenced promotional claims used to market products on Facebook.

FDA's letters provide evidence that the agency cares just as much about what a company says on its social media channels as on its website.

For example, in October 2014, FDA issued a Warning Letter to Vitalab, citing the company's Facebook posts which claimed its "Vit-Ra-Tox" products could be used to treat food poisoning, cholera, bacterial and parasitical infections, and heavy metals. Another Facebook post claimed a product would help the body to "repair broken bones."

None of these claims had been approved by FDA, the regulator wrote in its letter.

Similar claims were leveled against Florida-based NanoBiotech in February 2015. FDA said the company had been improperly marketing its NanobacTX and Urobac products since at least August 2013. In all, FDA cited eight Facebook posts by the company spanning 15 months.

Facebook posts weren't the only thing grabbing FDA's attention. Another online retailer was cited for including unapproved claims in the "About" section of its Facebook page that its products could help prevent cancer, treat infections and reduce inflammation.

A Big Batch of Letters, but Little Controversy

Notably, the four Warning Letters citing Facebook sent in late February represents FDA's largest-ever batch of letters citing Facebook. The agency's previous record was in September 2014, when it sent three in the same week.

Despite the high volume, FDA's latest letters avoid some of its most controversial interpretations of social media policy. For example, in February 2013 FDA issued a Warning Letter to a company citing its "Like" of an unapproved claim posted to the company's Facebook "wall." FDA said the "like" represented an endorsement of the claim. A similar letter citing an improper Facebook "like" was sent by FDA in July 2014.

FDA has not cited a "liked" status in its Warning Letters since July 2014.