With ingredients like bloodroot, shark cartilage and Cat’s Claw and assertions like “causes cancer cells to commit suicide,” it’s no wonder the Food and Drug Administration is taking notice.

On Tuesday, the agency warned 23 American companies and 2 foreign ones to stop claiming to prevent or cure cancer with their various “tablets, teas, tonics, black salves, and creams.”

Here are a few of the claims the agency cited:

— “Treats all forms of cancer”

— “80 percent more effective than the world’s number one cancer drug”

— “Skin cancers disappear”

— “Target cancer cells while leaving healthy cells alone”

— “Shrinks malignant tumors”

— “Avoid painful surgery, radiotherapy, chemotherapy, or other conventional treatments”

All told, 125 products were identified on the agency’s web site, www.fda.gov. Legal notices were sent to the companies urging prompt corrective action, which were also posted on the Web.

In the agency’s letter to Herbs for Cancer, an Arizona company that markets teas for more than a dozen cancers — from bladder and bone to malignant lymphoma — the agency shreds the company’s claims one by one. It also scolded that firm and others for deceptively spreading word about their products on the Web:

These claims are supplemented by use of the word “cancer” in most of your product names, as well as in the URL address for your website. Furthermore, the metatags used to bring consumers to your website include “cancer,” “herbs for cancer” and “fight-cancer.”

The site, herbsforcancer.com, has apparently been shut down, for unstated reasons.

In a matter of hours, the F.D.A.’s warnings have invaded Google search results, providing clear expressions of caution for anyone seeking more information on individual products like “C-Cell 4 Destroyer” and subjects like “herbs for cancer.”

Indeed, the effort was a strong sign that the agency was moving even more aggressively to counter fraud in the booming market for health advice and treatments on the Web. “Although promotions of bogus cancer ‘cures’ have always been a problem,” Margaret Glavin, the agency’s regulatory chief, said, “the Internet has provided a mechanism for them to flourish.”