WASHINGTON, D.C. -- The U.S. Food and Drug Administration is warning consumers to use 'extreme care' when buying products over the Internet that claim to diagnose, prevent, treat or cure H1N1.

The FDA issued the warning after purchasing and testing several products that were represented online as Tamiflu.

In one case, the product received contained no Tamiflu. Others did contain trace amounts but were not approved for use in the U.S.

Officials say patients who buy prescription drugs from Web sites operating outside the law are at increased risk of suffering adverse and possibly life-threatening side effects.

The FDA urges patients to buy only FDA-approved products from licensed pharmacies.

Tamiflu and Relenza have been approved for the treatment of H1N1.

Consumers can visit the FDA's website www.fda.gov for more information.