So-called fat dissolving treatments offered by spas do not eliminate fat and the companies should stop saying so, the U.S. Food and Drug Administration said on Wednesday.

The procedures, called by names such as lipodissolve, mesotherapy, lipozap, lipotherapy, or injection lipolysis all involve unproven injections of drugs, the FDA said in a statement.

"We are concerned that these companies are misleading consumers," Dr. Janet Woodcock, director of the FDA's Center for Drug Evaluation and Research, said in a statement.

"It is important for anyone who is considering this voluntary procedure to understand that the products used to perform lipodissolve procedures are not approved by the FDA for fat removal."

The agency issued warning letters to Monarch Medspa in King of Prussia, Pennsylvania; Spa 35 in Boise, Idaho; Medical Cosmetic Enhancements in Chevy Chase, Maryland; Innovative Directions in Health of Edina, Minnesota; PURE Med Spa in Boca Raton, Florida, and All About You Med Spa in Madison, Indiana.

The FDA also warned a Brazilian company that markets so-called lipodissolve products on two Web sites: zipmed.net and mesoone.com.

"The FDA will notify regulatory authorities in Brazil of this action," the FDA said in a statement.

"The agency has issued an import alert against the zipmed.net and mesoone.com entities to prevent the importation and distribution of unapproved lipodissolve drug products into the United States."

The treatments usually consist of injections of two drugs called phosphatidylcholine and deoxycholate, the FDA said.

"In some cases, other ingredients, including drugs or components of other products like vitamins, minerals and herbal extracts, are added to the mixture," the agency added. None has been shown to work in credible clinical trials, it said.