Sometimes, you just don't want to open the mailbox. It was precisely one of those days for shareholders of biopharmaceutical company United Therapeutics (NASDAQ:UTHR).

Before the opening bell this morning, United Therapeutics issued a press release noting that it had received a subpoena from the United States Department of Justice, represented by the U.S. Attorney's Office in Baltimore, examining the company's marketing practices of three FDA-approved drugs. The drugs in question are its Remodulin injection, Tyvaso inhalation solution, and Adcirca tablets, which are all indicated to treat pulmonary arterial hypertension, or PAH. This disease is characterized by high blood pressure in the arteries of the lungs, which makes the heart work harder than it needs to in order to pump blood throughout the body.

In its third-quarter results, released in late October, Remodulin, Tyvaso, and Adcirca combined for $300 million of United Therapeutics' $302.2 million in revenue. Keep in mind that investigations into marketing practices sometimes wind up with no evidence of wrongdoing, but can also lead to the opposite, such as in the case of Johnson & Johnson, which recently paid a $2.2 billion drug-marketing settlement just last month.

The subpoena itself requests United Therapeutics to supply documents related to each drug, and United Therapeutics has stated that it plans to cooperate fully with the investigation. Shares finished the day lower by less than 1%.

Fool contributor Sean Williams has no material interest in any companies mentioned in this article. You can follow him on CAPS under the screen name TMFUltraLong, track every pick he makes under the screen name TrackUltraLong, and check him out on Twitter, where he goes by the handle @TMFUltraLong.

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