WASHINGTON (AP) -- Federal regulators are ordering several companies to stop selling an unproven weight loss remedy that uses protein from the human placenta.

The Food and Drug Administration says it issued warning letters to seven companies that sell the protein as drops, pellets or sprays. The products are advertised as homeopathic remedies, or highly diluted drugs made from natural ingredients and sold with medical claims. Many doctors view homeopathic remedies as ineffective but mostly harmless because the drugs in them are present in such tiny amounts.

But the FDA said the products targeted Tuesday could be dangerous when taken as directed. The products contain human chorionic gonadotropin, which is a protein produced by the placenta and found in the urine of pregnant women.