SILVER SPRING, Md. — The Food and Drug Administration is warning consumers about a potentially harmful product represented as "Generic Tamiflu" that’s sold on the Internet.

There’s no FDA-approved generic drug for the prescription product Tamiflu, the agency reported Thursday. Tamiflu, made by Roche, is used to help prevent the spread of flu and alleviate flu symptoms.

The FDA said it bought the counterfeit "Generic Tamiflu" without a prescription from a Web site claiming to be an online drug store that is no longer operational, but the agency noted that the counterfeit Tamiflu is likely to be found for sale on other sites.

The fraudulent  "Generic Tamiflu" (above) doesn’t contain oseltamivir, the genuine drug’s active ingredient, according to the FDA.

FDA tests found that the fake product doesn’t contain Tamiflu’s active ingredient, oseltamivir, but instead contains cloxacillin, an ingredient in the same class of antibiotics as penicillin, the agency said.

People who are allergic to or may have experienced adverse reactions from penicillin products are at risk of experiencing similar reactions from cloxacillin — including a sudden, potentially life-threatening reaction called anaphylaxis, with symptoms that include difficulty breathing, chest tightness, swelling of the throat or tongue, hives, dizziness, loss of consciousness, or a rapid or weak pulse, according to the FDA. The agency said that so far it’s not aware of any reports of adverse reactions.

"A rogue Web site marketing drug products may look like a professional and legitimate Web site but may actually be an illegal operation," FDA commissioner Margaret Hamburg said in a statement. "Medicines purchased from web sites operating outside the law put consumers at increased risk due to a higher potential that the products will be counterfeit, impure, contaminated, or have too little or too much of the active ingredient."

The FDA said the counterfeit product it purchased arrived in an envelope postmarked from India that contained two foil-backed blister packages, each with 15 yellow-and-tan capsules containing white powder. The foil backing is printed and labeled in part, "Oseltamivir Phosphate 75mg. Capsules TM-FLU Capsules" and "Manufactured by: TRYDRUGS Pharmaceuticals PVT. LTD."

The FDA advises that anyone possessing or encountering any of these fraudulent Tamiflu drugs not to use them and to contact its Office of Criminal Investigations (OCI) at 1-800-551-3989 or go to the OCI web site at http://www.fda.gov/OCI.