(NewsNation) — The U.S. Food and Drug Administration wrote letters to eight companies, including CVS and Walgreens, warning them they were manufacturing, or marketing, unapproved eye products.

“These warning letters are part of the agency’s ongoing effort to protect Americans from potentially harmful ophthalmic products,” the FDA said in a Tuesday news release.

According to the FDA, eye products mentioned in the letters are “illegally marketed” to treat conditions such as: pink eye, cataracts, glaucoma and others. Some warning letters also cite companies for issues with product sterility.

These unapproved products pose a heightened risk of harm to users, as drugs applied to the eyes “bypass some of the body’s natural defenses,” the FDA said.

Some eye drug products were also labeled to say they contain silver, the FDA said. Long-term use of drugs with silver in them can cause some areas of the skin and other body tissues to permanently turn gray or blue-gray. Unapproved drugs can also cause consumers to delay or even stop safe, FDA-sanctioned medical treatments to cure, treat or prevent serious conditions, the agency said.

Companies who were sent letters are:

• Boiron Inc. 
• CVS Health 
• DR Vitamin Solutions
• Natural Ophthalmics, Inc.
• OcluMed LLC 
• Similasan AG/Similasan USA 
• TRP Company, Inc. 
• Walgreens Boots Alliance, Inc. 

A CVS spokesperson told NewsNation in a statement it stopped selling its CVS Health Brand Pink Eye Relief Eye Drops in stores and online. Customers who purchased the product can return it to CVS for a full refund, the spokesperson said.

“We’re committed to ensuring the products we offer are safe, work as intended and satisfy customers,” the company said in an emailed statement.

Walgreens also said it is pulling the products it was warned about, and that customers can return them for a full refund.

Kenneth Hansted, marketing director of Oclumed, said in an email the company takes the FDA’s warning letter seriously.

“We are committed to working with them to ensure that our eye drops are compliant and safe. For the past 14 years our customers’ health and safety have remained our highest priority,” he said. “We look forward to our continued track record of bringing efficacious, safe and quality over-the-counter products to the public.”

Similasan said in a statement that issues raised with its products and manufacturing were not due to consumer safety issues or incidents.

“We understand that the FDA shares our values of health and safety, and we are engaging with them to better understand the issues raised and provide updated documentation around our manufacturing processes,” the statement said. “We are cooperating with the FDA to have this matter resolved quickly.”

NewsNation has reached out to the other companies named in the FDA’s release for comment as well.

“The FDA is committed to ensuring the medicines Americans take are safe, effective and of high quality. When we identify illegally marketed, unapproved drugs and lapses in drug quality that pose potential risks, the FDA works to notify the companies involved of the violations,” Jill Furman, director of the Office of Compliance for the FDA’s Center for Drug Evaluation and Research, said in a statement. “We will continue to investigate potentially harmful eye products and work to ensure violative products stay off store shelves so that consumers can continue taking the medicines they need without concern.”