Despite the presence of cyanide groups, the pigment is not toxic to humans. Seniors among us will recognize “Prussian blue” as a crayon color.

Is Prussian blue harmful?

The most common side effects of Prussian blue are upset stomach and constipation. You can easily treat these side effects with other medications. You may have blue feces (stool) while you take Prussian blue.

What do you use Prussian blue for?

Prussian blue is used to treat radioactive cesium or thallium, or non-radioactive thallium poisoning. It works by combining with thallium and cesium in the intestines. The combination is then removed from the body through the stools.