FAST FACTS: Issue #6

Perchlorate and the Thyroid

While perchlorate is associated with reversible impacts on the thyroid gland, it is only at very high doses, hundreds or thousands of times higher than any amounts being detected in water supplies.

  • Credible studies show perchlorate’s direct effects on human health are limited to the thyroid. High levels of perchlorate can prevent the thyroid gland from absorbing iodide (which it needs to make hormones) from the bloodstream. This in itself is not dangerous however, because the body automatically compensates for this.
  • Perchlorate is not stored anywhere in the body, including the thyroid. Although there are no measurable effects when perchlorate is in the body at low levels, any effects of perchlorate on the body’s ability to produce hormones are fully reversible once exposure to high levels declines or stops.
  • According to a National Academy of Sciences’ (NAS) 2005 report and other credible, peer-reviewed studies by respected and independent medical researchers, low levels of perchlorate are not linked to thyroid problems or thyroid cancer in humans. The NAS report can be viewed at:;=NAP
  • The American Thyroid Association issued a press release on October 1, 2004, stating that various levels of perchlorate exposure were found not to be harmful to newborns, pregnant women and other adults.
  • Since the 1950s, perchlorate has been used in the U.S. and abroad to treat thyroid disorders. As a result, a wealth of information exists about perchlorate and how it relates to human health. The doses used as a medicine are tens of thousands of times greater than one could get from the low levels of perchlorate being detected in drinking water today.