Background: There is little information on the effectiveness of therapies for severe chronic constipation. In a phase 3 trial, we previously demonstrated that a vibrating capsule was significantly more efficacious than a placebo in chronic constipation., Aim: To examine the effects of a vibrating capsule and placebo on symptoms and health-related quality of life (HRQoL) in patients with severe chronic constipation., Methods: We performed a post hoc analysis of phase 3, multicentre, randomised, double-blind, and placebo-controlled 8-week clinical trial of a vibrating capsule to specifically assess outcomes among subjects who reported 0 complete spontaneous bowel movements (CSBMs) during the 2-week baseline period. We assessed effects of treatment on bowel symptoms, patient satisfaction, and HRQoL. CSBM responders were defined as subjects with increases of ≥1 or ≥2 or ≥3 weekly CSBMs (CSBM1 or CSBM2, CSBM3, respectively) over baseline for ≥6 out of 8 weeks of treatment., Results: The severe chronic constipation subgroup comprised 175 (56%) of the 312 subjects. Significantly more subjects with severe chronic constipation who received the vibrating capsule than those who received the placebo were CSBM1 (44.9% vs. 20.9%, p = 0.007), CSBM2 (29.2% vs. 11.6%, p = 0.004), and CSBM3 (19.10% vs 6.98%, p = 0.017) responders. Straining effort, stool consistency, patient satisfaction, and HRQoL significantly improved in the severe chronic constipation subgroup. A mild vibrating sensation was reported in 10%., Conclusion: The vibrating capsule significantly improved constipation-related symptoms and HRQoL in patients with severe constipation, affirming its efficacy and safety across the spectrum of chronic constipation., (© 2024 The Author(s). Alimentary Pharmacology & Therapeutics published by John Wiley & Sons Ltd.)