The US Food and Drug Administration (FDA) is cracking down on companies that sell products claiming to remove heavy metals and other “toxins” from the body. Yesterday, eight companies that market over-the-counter chelation products received letters from the FDA warning that they were making unproven claims about the ability of their drugs to treat a range of conditions from Alzheimer’s disease to autism spectrum disorder.

Chelation therapy involves the administration of a chelating agent — the most commonly used compound is ethylenediaminetetraacetic acid, or EDTA. The chelating agent binds to heavy metals in the body, making them less reactive and allowing them to pass through the urine. The FDA has approved chelation therapy only for treating exposure to toxic levels of heavy metals like lead and plutonium, and also for interstitial cystitis, a chronic inflammation of the bladder wall.

There have been scattered studies suggesting that chelation therapy could be effective in treating certain neurodegenerative diseases, especially Alzheimer’s disease. It’s theorized that the amyloid plaques in the brain thought to cause Alzheimer’s disease may result from an accumulation of metals like zinc or copper in the brain.

One chelating agent that’s currently being tested against Alzheimer’s disease is clioquinol, a drug initially used to treat indigestion in the 1930s. It was pulled off the market in 1985 after it was shown to cause a condition called subacute myelo-optic neuropathy, which resulted in, among other things, paralysis and blindness. Australian pharmaceutical company Prana Biotechnology is currently conducting Phase II trials examining the efficacy of clioquinol in treating Alzheimer’s. Clioquinol has also been shown to somewhat mitigate the symptoms of Huntington’s disease in mice.

But many claims about chelation therapy remain stubbornly unproven. A review of the literature on chelation therapy and coronary artery disease by the American Heart Association “found no scientific evidence to demonstrate any benefit from this form of therapy”.

Alternative medicine practitioners claim that the ‘cleansing’ properties of chelating agents can treat or prevent a number of serious conditions. Evenbetternow, one of the companies that received a warning letter, sells liquids, capsules, and even clay baths containing EDTA. That’s likely to change now.