Polyethylene Glycol (PEG) is scientifically validated for use in the management of constipation, including cases associated with spastic colon (commonly referred to as irritable bowel syndrome with constipation, or IBS-C). PEG is an osmotic laxative that works by retaining water in the stool, resulting in softer stools and increased frequency of bowel movements. Multiple randomized controlled trials and meta-analyses have demonstrated PEG's efficacy and safety for treating chronic constipation in adults and children. In patients with spastic colon, who often experience alternating bowel habits including constipation, PEG is recommended by clinical guidelines as a first-line therapy for constipation relief.

A 2016 meta-analysis published in Alimentary Pharmacology & Therapeutics concluded that PEG is significantly more effective than placebo in increasing stool frequency and improving stool consistency in patients with chronic constipation, including those with IBS-C. The American College of Gastroenterology and other professional societies endorse PEG as a preferred osmotic laxative due to its favorable safety profile, minimal systemic absorption, and low risk of electrolyte disturbances.

While PEG does not address the underlying motility disorder or abdominal pain in spastic colon, its use is justified for symptomatic treatment of constipation, which is a prominent and troublesome feature in many patients with this diagnosis.