INTRODUCTION
Constipation is commonly treated with over-the-counter (OTC) products whose efficacy and safety remain unclear. We performed a systematic review of OTC therapies for chronic constipation and provide evidence-based recommendations.

METHODS
We searched PubMed and Embase for randomized controlled trials of ≥4-week duration that evaluated OTC preparations between 2004 and 2020. Studies were scored using the US Preventive Services Task Force criteria (0-5 scale) including randomization, blinding, and withdrawals. 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).

RESULTS
Of 1,297 studies identified, 41 met the inclusion criteria. 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. Diarrhea, nausea, bloating, and abdominal pain were common adverse events, but no serious adverse events were reported.

DISCUSSION
The spectrum of OTC products has increased and quality of evidence has improved, but methodological issues including variability in study design, primary outcome measures, trial duration, and small sample sizes remain. We found 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 validation with more rigorously designed studies is warranted.

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