Polyethylene glycol (PEG), particularly in the form of PEG 3350, is an osmotic laxative commonly used to treat constipation. In the context of Irritable Bowel Syndrome (IBS), PEG is primarily used to manage the constipation-predominant subtype (IBS-C). PEG works by retaining water in the stool, resulting in softer stools and promoting bowel movements.

Several randomized controlled trials and systematic reviews have evaluated PEG's efficacy in treating IBS-C. These studies generally show that PEG is effective in improving stool frequency and consistency in IBS-C patients. However, the evidence is less robust regarding its effects on the broader symptom complex of IBS (such as abdominal pain, bloating, and overall quality of life). For example, a 2014 meta-analysis (Am J Gastroenterol) concluded that while PEG is effective for constipation symptoms, it does not significantly improve global IBS symptoms. Most clinical guidelines, such as those from the American College of Gastroenterology, recommend PEG as a first-line therapy for constipation in IBS-C but note that it is not specifically a treatment for the core symptoms of IBS.

In summary, PEG’s use in IBS is scientifically validated for addressing constipation, but not for the full spectrum of IBS symptoms. The evidence supporting its use for constipation in IBS is moderate, leading to a rating of 3 out of 5.