Black psyllium (Plantago indica) is used primarily for its high soluble fiber content, similar to the more commonly known blonde psyllium (Plantago ovata). Scientific evidence supports the use of psyllium (including black psyllium) for promoting rectal and overall colon health, particularly in relation to bowel regularity and the management of constipation. Psyllium's fiber absorbs water and forms a gel-like mass, which increases stool bulk and moisture, thereby softening stools and making them easier to pass. This action is especially beneficial for individuals with hemorrhoids or anal fissures, as softer stools reduce straining and irritation in the rectal area.

Clinical studies have shown that psyllium supplementation is effective for improving stool frequency and consistency in individuals with chronic constipation and irritable bowel syndrome (IBS). The fiber's ability to normalize bowel movements also helps prevent both constipation and diarrhea. Furthermore, some studies suggest that regular intake of psyllium may reduce the recurrence of hemorrhoids and assist in their management by minimizing trauma to the rectal mucosa during defecation.

While most research focuses on blonde psyllium, black psyllium contains similar active components and is used interchangeably in some regions. The U.S. Food and Drug Administration and other regulatory bodies recognize psyllium's efficacy for bowel regulation. Thus, the use of black psyllium to support rectal health is grounded in scientific evidence, particularly related to its role as a bulk-forming laxative.