The FDA has issued a warning letter to OCLO Nanotechnology Science, a Florida-based biotech, for selling unapproved drug products marketed as COVID-19 treatments.

The unapproved chlorine dioxide products include OCLO 3000, marketed as an antiviral immune booster, “misleadingly” represented as safe and effective for treating or preventing COVID-19, the agency said.

The agency noted that it is illegal to advertise that a drug can treat a disease unless it is approved based on “competent and reliable scientific evidence,” but no such study is currently known to exist for the products in question.