The study evaluated whether the addition of linaclotide to an oral sulfate solution (OSS) would improve bowel preparation for colonoscopy in 370 outpatients in a randomized controlled trial. Patients were divided into three groups: OSS + linaclotide, OSS and polyethylene glycol (PEG). The primary endpoint – adequate rate of bowel preparation – did not show a statistically significant difference between OSS + linaclotide (86.5%) and OSS (88.0%; RR 0.98, 95% CI 0.89–1.08, p=0.723). Both OSS + linaclotide and OSS groups had significantly higher adequate preparation than PEG (86.5% vs. 73.9%, p=0.013; 88.0% vs. 73.9%, p=0.005). In an exploratory analysis, bloating was less common in the OSS + linaclotide group (4.0%) versus OSS (16.0%) and PEG (11.8%, p=0.007), with no differences in other adverse events. No differences were found in tolerability, colonoscopy findings, or safety. The study did not meet the primary objective, linaclotide did not add cleaning efficacy to OSS versus PEG.