Guaiac is not used therapeutically to treat or support blood in stool; rather, it is employed as a diagnostic tool in medicine. The guaiac-based fecal occult blood test (gFOBT) is a well-established laboratory method for detecting hidden (occult) blood in stool samples. This test relies on the peroxidase-like activity of hemoglobin, which catalyzes the oxidation of guaiac resin in the presence of hydrogen peroxide, resulting in a blue color change if blood is present. The scientific basis for using guaiac in this diagnostic context is robust and has been validated for decades in clinical practice. Numerous studies and clinical guidelines support the use of guaiac-based tests for colorectal cancer screening and for identifying gastrointestinal bleeding.

However, it is important to note that guaiac is not used as a treatment or support for blood in stool; it does not address the underlying condition but merely serves as a chemical reagent to detect the presence of blood. Its use is purely diagnostic, not therapeutic or supportive. Thus, the scientific evidence for its use as a diagnostic agent to detect blood in stool is strong (rated 5), but there is no evidence or rationale for its use as a treatment or supportive ingredient for the condition itself.