A patient who seeks medical help for overactive tear ducts shouldn’t be surprised if the doctor prescribes Botox, a drug typically reserved for removing facial frown lines.

Doctors often use this pharmaceutical strategy, called off-label prescribing, based on evidence that many drugs can do more than their narrow purposes approved by the U.S. Food and Drug Administration (FDA).

However, drug companies are legally barred from advertising the alternative uses, despite published or practice-based evidence that they work. The reason lies in decades-old restrictions by the FDA banning off-label promotion.

In the past, companies like Pfizer, Astra Zeneca and Eli Lilly have been fined billions of dollars for allegedly violating the FDA’s rules, and some salesman and manufacturers have been taken to court on criminal charges, reports the Wall Street Journal. Now, a few pharmaceutical giants are taking to the courts to change the FDA’s restrictions, claiming that the rules limit a drug company’s right to free speech in its advertising.

The FDA’s stance is simply that prescribing medications for unapproved uses puts patients at risk.

“FDA does not want pharmaceutical companies promoting something as safe and effective when that hasn’t been proven,” Thomas Abrams, director of the FDA’s Division of Drug Marketing, Advertising and Communications, told the Wall Street Journal. “Think of someone you love the most. Would you want that person on a drug that’s not proven simply because the drug was promoted in such a way?”

The drug companies’ motivations do make economical sense, said David Kroll, professor of pharmaceutical sciences at North Carolina Central University. It’s not always cost-effective for a drug company to undergo the FDA’s lengthy approval process for a second use for an already approved drug, particularly if evidence shows that the drug’s off-label use is safe and effective.

“The FDA is erring far more on the side of safety, and drug companies want the freedom to make as much revenue as possible,” Kroll said. “Probably the proper middle ground is if there’s published clinical data in a top quality peer-reviewed journal, there should be some allowance for advertising off-label uses.”

Many doctors use drugs that pull this kind of double duty. For instance, the erectile dysfunction drug, Viagra, can also increase blood flow to other parts of the body to help heal meningitis or avoid amputation. The drug known as Lumigan is an eye drop for glaucoma, but its twin Latisse is prescribed to help grow fuller, more luscious eyelashes.  Even the illicit drug Ecstasy may hold promise for patients with post-traumatic stress disorder.