Background: Temstem is a mobile application developed in cooperation with voice-hearing persons to help them cope with distressing voices. After psychoeducation about voice hearing, Temstem offers two functions: Silencing is a mode designed to inhibit voice activity through the processing of incompatible language; the Challenging mode introduces dual tasking (as used in eye movement desensitisation and reprocessing) designed to reduce the emotionality and vividness of a voice memory. Two different language games, Lingo Tapper and Word Link, are provided, containing both functions. This study aimed to explore the momentary effects of Temstem on voice-hearing distress, emotionality and vividness in a naturalistic sample of voice-hearing app users. Method: Temstem is freely available in the Netherlands. We collected data through the app from 1048 individual users who had given informed consent for the study. We assessed changes in pre- and post-session scores on distress, emotionality and vividness, and we evaluated differences in outcomes between the games and whether effects remained stable over multiple sessions. Results: Users had been hearing voices for an average of 4.95 years; 79 % had been informed about Temstem by a mental health therapist or coach. After a Silencing session, voice-hearing distress was reduced, t(958) = 27.12, p < .001, d = 0.49; the degree of reduction remained stable after repeated use, F(1, 7905.57) = 1.91, p = .167. After a Challenging session, emotionality, t(651) = 23.16, p < .001, d = 0.74, and the vividness of voice memories were reduced, t(651) = 22.20, p < .001, d = 0.71; both diminished slightly with frequent use, F(1, 2222.86) = 7.21, p < .05; F(1, 2289.92) = 4.25, p < .05. In comparison with Lingo Tapper, larger reductions were seen for a Word Link game: emotionality t(226) = 2.88, p < .005, d = 0.21; vividness t(226) = 2.29, p < .05, d = 0.17. Discussion: In this heterogeneous sample of voice-hearing individuals, Temstem appeared to be a promising coping tool; momentary voice-hearing distress and the emotionality and vividness of voice statements were reduced after a Temstem session. Despite important limitations and the need for more research, naturalistic studies of user app data may yield interesting and generalisable findings.@en