There are many possible causes of and contributors to constipation, which means the reason for constipation varies from person to person.
A number of health conditions can cause constipation, including hypothyroidism, diabetes, hypercalcemia, intestinal stricture, multiple sclerosis, and Parkinson’s disease. Constipation can also be caused by various medications, including opioids, iron supplements, nonsteroidal anti-inflammatory drugs (NSAIDs), calcium channel blockers, antacids, antihistamines, and diuretics.
Lifestyle factors that may increase the risk of constipation include a low fiber intake,[1][2][3][4] physical inactivity,[2][5][6][4] and a low fluid intake,[7][8][9][4] although conflicting evidence exists for each of these factors.