Dieters claim HCG helps them lose weight, without exercising or feeling hungry. Millions of HCG products are sold online and in stores as pellets, sprays or oral drops.
The FDA and Federal Trade Commission issued warning letters to seven companies, saying those products are unapproved, and therefore illegal.
They want other companies and clinics to take notice.
"There are no HCG products approved by the FDA for weight loss," said Elizabeth Miller, FDA.
The FDA first ruled on HCG's legality after a News 8 report in February. As a result of our investigation, several North Texas health and vitamin stores pulled it from their shelves. The products are still being marketed and sold across North Texas and the United States
The FDA has not taken action against manufacturers or retailers, until now.
"This is a pretty landmark situation," said Tammy Beaumont, Methodist Dallas Weight Management Institute.
She applauds the FDA's action.
"I think it's great," Beaumont said. "I think it's the first time that our government has really said, 'Hey, you have to do something sensible. These jack-in-the-box kind of fixes aren't going to make healthy people.'"
The FDA warnings target so-called homeopathic HCG. Homeopathic means highly diluted. But, federal authorities said no matter how small the quantity, HCG is not approved for weight loss.
HCG, or human chorionic gonadotropin, is FDA approved for other medical uses, including fertility treatments.
Some doctors also prescribe it, off label, for weight loss. But marketing a drug for an unapproved purpose is also illegal.
In fact, the Texas Attorney General recently ordered several North Texas weight-loss clinics to change how they advertise HCG.