Lubricant laxatives. These contain mineral oil, which stays inside the intestine, coats the stool particles, and apparently prevents the water from leaving the stool, which results in softer stool. Long-term use of this type of laxative can cause several problems. The most common is that the oil can absorb fat-soluble vitamins from the intestine, which could lead to deficiencies. In pregnant women, this could be a major problem. People who have trouble swallowing may accidentally get some of the oil in their lungs, which could cause lipid pneumonia. Mineral oil may also decrease the absorption of some drugs (such as birth control pills), which decreases their effectiveness.

Emollient laxatives (stool softeners). Stool softeners contain a compound called docusate, which is a wetting agent that helps water in the colon penetrate and mix with stool, resulting in a softened stool. Docusate has not proven to be a consistent remedy for relief, however, but stool softeners are often used for long-term treatment. Docusate may take a week or more to be effective, with doses increasing after a week or two if nothing has happened. Generally considered safe, docusate may allow mineral oil and some medications to be absorbed from the intestine. Absorbed mineral oil collects in body tissues, such as the lymph nodes and the liver, where it causes inflammation. While the consequences of this inflammation are not clear, the general consensus is that prolonged absorption of mineral oil should be avoided.

Hyperosmolar laxatives. These are undigestible, unabsorbable compounds that remain in the colon and retain the water already there, which again, results in stool softening. The most common hyperosmolar laxatives are lactulose, sorbitol, and polyethylene glycol. Available by prescription only, they are safe for long-term use with few side effects. Colonic bacteria may digest hyperosmolar laxatives and turn them into gas, which may result in unwanted abdominal bloating and flatulence. However, gas can be reduced by reducing the dose of the laxative, and some people find that the gas decreases over time.

Saline laxatives. These contain non-absorbable ions such as magnesium, sulfate, phosphate, and citrate, which remain in the colon and draw water into it. The water softens the stool. Magnesium can also have mild stimulatory effects on the colonic muscles, but it can be partially absorbed into the body from the intestine. Magnesium is removed from the body through the kidneys, so people with impaired kidney function could develop toxic levels of magnesium from long-term use of laxatives containing magnesium. The most frequently-used and mildest of these laxatives is milk of magnesia, while Epsom salts is more potent and contains magnesium sulfate.

Note: Statements in this article may not be approved by the FDA, and should not be considered as professional medical advice.