The FDA has issued warnings and advisory letters to 17 companies that it says are illegally selling products that claim to prevent, treat, or cure Alzheimer’s as well as other serious diseases. The agency cited more than 58 dietary supplements, tablets, capsules, and oils that had not been reviewed for safety or shown to improve the conditions they purport to treat.

Currently, about 5.5 million Americans age 65 or older suffer from Alzheimer’s disease.

“These products may be ineffective, unsafe and could prevent a person from seeking an appropriate diagnosis and treatment,” the FDA warned. They may also mislead consumers into thinking therapies to cure Alzheimer’s exist, when there is currently no known cure.

The ingredients in the products ranged from benign substances such as Vitamin D, green tea extract, melatonin, and fish oil to potentially riskier herb, mineral, and botanical mixtures. Companies that received warnings included Earth Turns, TEK Naturals, John Gray’s Mars Venus, Blue Ridge Silver, and Gold Crown Natural Products (see the full list here).

Currently, about 5.5 million Americans age 65 or older suffer from Alzheimer’s disease, and the Department of Health and Human Services expects that number to grow in the coming years as the population ages.

Meanwhile, over half of American adults take dietary supplements, and in the case of vitamins and herbs, these supplements are often beneficial. However, a recent study found that some 776 over-the-counter supplements contained unapproved drug ingredients.

The FDA encourages consumers to stay alert and report suspected scams. In the meantime, the companies cited have 15 days to respond to the agency’s warnings.