The celebrity posted a selfie last month holding up a branded bottle of the pills alongside text endorsing their effects.
The medicine?s maker, Duchesnay, later confirmed it had compensated the TV star for ?sharing her experience?.
Ms Kardashian?s Twitter account has more than 34 million followers
But the Food and Drinks Administration has attacked the posts for failing to flag potential side effects.
It has ordered the firm to stop promoting its product in this manner.
Ms Kardashian?s posts talked of her own use of the drug Diclegis, before stating: ?Most importantly, it?s been studied and there was no increased risk to the baby.?
She provided a link to the drug firm?s own related safety warnings, but did describe the potential risks herself.
One side effect of a normal dose of the drug is drowsiness. An overdose can cause vertigo, mental confusion and an abnormal heart rate.
?The social media post is misleading because it presents various efficacy claims for Diclegis, but fails to communicate any risk information,? FDA division director Robert Dean wrote in a complaint to the Canadian pharmaceutical manufacturer.
?Because the violations described above are serious and repeated, we request, further, that your submission includes a comprehensive plan of action to disseminate truthful, non-misleading, and complete corrective messages about the issues discussed in this letter to the audiences that received the violative promotional materials.?
He added that the correction should be distributed ?using the same media? as the original messages, indicating that the warnings should appear on Ms Kardashian?s social media accounts.
The celebrity?s selfie has since been deleted from Instagram and Facebook ? although a tweet alluding to the posts remains online.
Ms Kardashian could not be reached for comment.
But the drugs firm said that it would issue a formal response ahead of a 21 August deadline.
?We will take quick action in responding to the FDA?s letter and immediately and effectively address any issues,? a spokeswoman told the BBC.
?We appreciate the FDA?s objective of ensuring that promotions remain consistent with approved labelling and fully support this objective.?
It is illegal to advertise prescription medicines to the public in the UK, and Diclegis is not currently available in the country.
However, the Royal Pharmaceutical Society has raised concerns.
?Social media is a global phenomenon and people in the UK may well follow US celebrities social media accounts,? commented the society?s communications chief, Neal Patel.
?Prescription medicines licensed in the US may not be available in the UK, which can lead people to searching for products online and then ordering medicines from dubious sources putting their health at risk.
?The best advice is to consult a health professional if you have a health concern, including morning sickness. Our job is to make sure people get safe effective treatment.?