In a publication in The American Journal of Gastroenterology, Rao et al searched PubMed and Embase for randomized, controlled trials with a duration of 4 weeks or longer evaluating OTC preparations between 2004 and 2020. Of the 1,297 studies the researchers found, 41 met the inclusion criteria. The investigators used the U.S. Preventive Services Task Force criteria to score the studies by randomization, blinding, and withdrawals. According to the authors, the strengths of evidence were adjudicated within each therapeutic category, and recommendations were graded (A, B, C, D, and I) based on the level of evidence (level I, good; II, fair; or III, poor).

They found that there was good evidence (grade A recommendation) for the use of the osmotic laxative polyethylene glycol (PEG) and the stimulant senna; moderate evidence (grade B) for psyllium, SupraFiber, magnesium salts, stimulants (bisacodyl and sodium picosulfate), fruit-based laxatives (kiwi, mango, prunes, and ficus), and yogurt with galacto-oligosaccharide/prunes/linseed oil; and insufficient evidence (grade I) for polydextrose, inulin, and fructo-oligosaccharide. The most common adverse effects were diarrhea, nausea, bloating, and abdominal pain, but no serious adverse events were reported.

They concluded that PEG and senna are the only OTC laxatives with level I evidence and grade A recommendations for the treatment of constipation, although PEG is the only one supported by both short- and long-term studies. They also noted that other laxatives had grade B recommendations such as psyllium, SupraFiber, magnesium-rich water, magnesium oxide, diphenylmethane stimulants (bisacodyl and sodium picosulfate), fruit-based laxatives (kiwi, mango, prunes, and ficus), and yogurt plus galacto-oligosaccharide, prunes, and linseed oil. The authors wrote that the range of OTC products has expanded and quality of evidence has improved, but methodological issues including variability in study design, primary outcome measures, trial duration, and small sample sizes remain.

The researchers said that they discovered good evidence to recommend polyethylene glycol or senna as first-line laxatives and moderate evidence supporting fiber supplements, fruits, stimulant laxatives, and magnesium-based products. For others, further confirmation with more thoroughly designed studies is warranted. According to the authors, for these and other alternative products, there is a clear need for more comprehensive, high-quality studies using standardized endpoints.

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