The U.S. Food and Drug Administration (FDA) has issued a new round of warnings and advisory letters to makers of dietary supplements, telling them not to falsely claim their products cure, prevent or treat serious diseases. Last year the FDA and the Federal Trade Commission (FTC) sent warning letters to makers and distributors of 12 products sold as treatments for opioid addiction and withdrawal.

The current letters are aimed at the makers of supplements that promise to prevent or treat Alzheimer’s disease and other serious health conditions, Fortune reports. In a statement, FDA Commissioner Scott Gottlieb said, “We’ve also taken action in recent years against companies and dietary supplements making similar claims for the treatment of serious conditions such as cancer and opioid addiction. Although these companies may have stopped selling the products or making unproven claims, numerous unsafe and unapproved products continue to be sold directly to consumers due in part to the ease with which companies can move their marketing operations to new websites.”

In January 2018, the FDA and FTC sent letters to makers of products such as “Opiate Freedom 5-Pack,” “Withdrawal Support,” “Opiate Detox Pro” and “AddictaPlex.”