A bulk-forming laxative is a laxative that works by absorbing water and swelling in the bowel, increasing stool volume and softness to stimulate normal peristalsis. Typical agents include psyllium husk, methylcellulose, and wheat bran, all rich in soluble or insoluble fibre. They are considered the gentlest class of laxatives and are used for chronic constipation, irritable bowel syndrome, and during pregnancy, provided fluid intake is adequate. Without enough water they can cause blockage, so they must be taken with plenty of liquid. Their action mimics the effect of a high-fibre diet, and they are often the first-line choice for long-term use.