The letter warns Duchesnay that the social media posts on the celebrity's various accounts violates the agency's drug promotion rules, according to the Associated Press.
Although the post links to the company website, which has the FDA-required labeling information, the agency says it's not enough and fails to list the possible side effects of the drug.
The agency also specifically notes in the letter that the post does not warn that Diclegis is not approved for women with a form of prolonged vomiting that causes dehydration.
Kardashian's post talks about battling nausea during her pregnancy – trying everything to help it without any positive results until she started taking Diclegis.
This is not the first time the company has come under fire by the FDA. According to the letter, they sent a letter to doctors without including the risk information, which prompted a similar letter in 2013.