The Food and Drug Administration announced a crackdown on a controversial therapy against the makers of over-the-counter chelation products which supposedly help “cleanse” the body.

The products regularly sold on the internet are advertised as a treatment for autism, Alzheimer's disease and Parkinson's disease. Letters of warning were sent out to these companies by the FDA notifying them that the substances they sell without a prescription for a procedure known as "chelation" are "unapproved drugs and devices," and violates federal law.

"What we're telling consumers is that any chelation therapy marketed over the counter is suspect," Michael Levy, director of the FDA's Division of New Drugs and Labeling Compliance, said during a briefing with reporters.

The products are often sold as dietary supplements promoting their alleged health benefits. Products come in various dosages and forms, including suppositories, capsules, liquid drops, sprays and clay baths.

The substances in these drugs may lead to serious health complications which include dehydration, kidney failure and in serious cases could even result in death.

According to the FDA, chelation has been used by doctors to treat patients exposed to dangerous levels of heavy metals. For the treatment, patients are infused with compounds that bind to the metals, enabling the metals to be excreted.

The chelation products approved by the FDA are not available over the counter and can only be administered by a trained professional because of the related risks.

The warning letters were sent to: World Health Products; Hormonal Health; Evenbetternow; Maxam Nutraceutics/Maxam Laboratories; Cardio Renew; Artery Health Institute; and Dr. Rhonda Henry.