BackgroundGuidelines encourage GPs to make brief opportunistic interventions to support weight loss. However, GPs fear that starting these discussions will lead to lengthy consultations. Recognising that patients are committed to take action could allow GPs to shorten brief interventions.AimTo examine which patient responses indicated commitment to action, and the time saved if these had been recognised and the consultation closed sooner.Design and settingA mixed-method cohort study of UK primary care patients participating in a trial of opportunistic weight management interventions.MethodConversation analysis was applied to 226 consultation audiorecordings to identify types of responses from patients that indicated that an offer of referral to weight management was well received. Odds ratios (OR) were calculated to examine associations between response types and likelihood of weight management programme attendance.ResultsAffirmative responses, for example ‘yes’, displayed no conversational evidence that the referral was well received and showed no association with attendance: ‘yes’ (OR 1.2, 95% confidence interval [CI] = 0.37 to 3.95, P = 0.97). However, ‘oh’-prefaced responses and marked positive responses, for example ‘lovely’, showed conversational evidence of enthusiasm and were associated with higher odds of commercial weight management service attendance. Recognising these could have saved doctors a mean of 31 seconds per consultation.ConclusionWhen doctors make brief opportunistic interventions that incorporate the offer of help, ‘oh’-prefaced or marked positive responses indicate enthusiastic acceptance of the offer and a higher likelihood of take-up. Recognising these responses and moving swiftly to facilitate patient action would shorten the brief intervention in many cases.