Misconceptions about Laxatives
Widely used but frequently misunderstood
Patients are always searching for the best laxative. Because laxatives are one of the most widely available over-the-counter medications available, and because such a large percentage of the population have used or plan to use laxatives, a large number of misconceptions about OTC laxatives have arisen over the years.
|
|
|
The general consensus amongst physicians is that most laxatives are safe for use in the short term, and many are safe even if taken over a longer period of time, although the on-label usage does not indicate so except for Amitiza (or technically known as lubiprostone). Chief amongst these misconceptions about laxatives include four claims: (1) that a certain type of laxative causes nerve damage in the gut, (2) that chronic usage predisposes one to cancer, (3) that laxatives cause intolerance and eventually resistance to medication.
The myth of nerve damage
Does the best laxative cause intestinal nerve damage? The lining of the intestine is richly endowed with nerves of all sorts. There have been suggestions that these intestinal nerves can be damaged by intake of anthraquinone laxatives. The anthraquinone laxatives, found in herbal preparations and other OTC forms, include the senna plant. Very early studies have noted that in colonic tissue removed from patients with severe constipation that there was discoloration, damage to nerves and atrophy smooth muscles. These patients had also take laxatives chronically over long periods of time. However, these studies were not well controlled. In other words, some people associate the nerve and muscle impairment to laxatives, but it may be true that in people with severe constipation, there is already a natural, high incidence of intestinal nerve damage. Indeed, in a better controlled study comparing patients who had taken anthraquinones and those who did not, results showed little difference in nerve tissue that was accessible by colonoscopy.
The myth of cancer
Do laxatives cause cancer? If one picks out the best laxative, is it going to fix constipation at the expense of something much more life threatening? With respect to anthraquinones, there have also been reports in animal studies that anthraquinones seem to induce mutations that lead to cancer. However, one should always keep in mind that the animal studies are usually done with very high doses of anthraquinones. Similar studies using animals have shown that toxins in peanut butter, and in artificial sweeteners, used at very high doses, can also lead to cancer. Yet people continue to eat peanut butter and artificial sweeteners, with little epidemiological evidence showing that they are raising cancer rates. Extensive statistical analysis has revealed weak links between anthraquinone intake and colorectal cancer, but these links have tended to disappear upon reanalysis on larger data sets. It seems that the link to cancer is overstated and perhaps non-existent, although this continues to be an area of active research.
Laxative abuse and tolerance
Do laxatives cause tolerance? Tolerance means that a patient would have to take his best laxative more and more to achieve the same constipation-relieving effect. In animal research, the reports are conflicting. In some studies with guinea pigs, rhein, bisacodyl and phenolphthalein-based laxatives showed that the guinea pigs seem to show tolerance over the period of 10 days. Alternatively, in studies with rats, chronic laxative use had no effect on response. Moreover, in reports with humans, certain spinal cord patients have taken bisacodyl-based laxatives for periods up to 34 years, and have exhibited no loss of therapeutic response. However, interviews with some patients suggest that at least patients self-reported increased laxative dose was necessary for maintaining desired effect. The bottom line is that there are at least some people who have taken laxatives for decades with no signs of tolerance.
Sources:
Muller-Lissner et al, Myths and Misconceptions about Constipation, American Journal of Gastroenterology, 2005, 100:232-242