Kim Kardashian got a drug-maker into trouble.

The Food and Drug Administration (FDA) in the United States has sent a warning letter to the drug-maker over the reality TV star's endorsement of its pills for morning sickness.

Last month on Instagram, Twitter and Facebook, Kardashian, who is pregnant with her second child, vouched for a medication called Diclegis, made by privately held Pennsylvania pharmaceutical company Duchesnay.

In her post, she holds up a bottle of the drug and said it helped her with her morning sickness. She said she was "partnering" Duchesnay to raise awareness of morning sickness and urged her millions of social media followers to ask their doctors about the drug. The company later sent out a press release about the partnership.

The endorsement failed to include the necessary risk information and did not note limitations on the drug's use.

According to the FDA, that makes it misleading. The messages did include links to webpages where more complete safety information was available, but the regulator says that was not sufficient.

The FDA letter, dated last Friday, asked Duchesnay to "immediately cease misbranding" the drug or stop selling it. It has given the company until Aug 21 to respond.

In an e-mail message, a Duchesnay spokesman said the company "acknowledges that its communications, including in social media as in this particular instance, need to be in accordance with applicable rules and regulations".

Duchesnay "will take quick action in responding to the FDA's letter and immediately and effectively address any issues".

Diclegis is suggested for women who do not respond to more conservative measures to address morning sickness, such as eating more small meals or bland foods.

It is controversial because an earlier version of the compound known as Bendectin was withdrawn from the US market in 1983 over fears that it could cause birth defects, though the FDA later concluded that those concerns were unfounded.

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