BackgroundTelemedicine is a strategy for overcoming barriers to access evidence-based psychotherapy. Digital modalities that operate outside session-based treatment formats, such as ongoing two-way messaging, may further address these challenges. However, no study to date has established suitability criteria for this medium.MethodsA large outpatient sample (n = 10,718) engaged in daily messaging with licensed clinicians from a telemedicine provider. Patients consisted of individuals from urban and rural settings in all 50 states of the US, who signed up to the telemedicine provider. Using a longitudinal design, symptoms changes were observed during a 12 week treatment course. Symptoms were assessed from baseline every three weeks using the Patient Health Questionnaire (PHQ-9) for depression, and the Generalized Anxiety Disorder (GAD-7) for anxiety. Demographics and engagement metrics, such as word count for both patients and therapists, were also assessed. Growth mixture modeling was used to tease apart symptoms trajectories, and identify predictors of treatment response.ResultsTwo subpopulations had GAD-7 and PHQ-9 remission outcomes (Recovery and Acute Recovery, 30.7% of patients), while two others showed amelioration of symptoms (Depression and Anxiety Improvement, 36.9% of patients). Two subpopulations experienced no changes in symptoms (Chronic and Elevated Chronic, 32.4% of patients). Higher use of written communication, patient characteristics, and engagement metrics reliably distinguished patients with the greatest level of remission (Recovery and Acute Recovery groups).ConclusionsRemission of depression and anxiety symptoms was observed during delivery of psychotherapy through messaging. Improvement rates were consistent with face-to-face therapy, suggesting the suitability of two-way messaging psychotherapy delivery. Characteristics of improving patients were identified and could be used for treatment recommendation. These findings suggest the opportunity for further research, to directly compare messaging delivery with a control group of treatment as usual.Trial registrationClinicaltrials.gov Identifier: NCT03699488, Retrospectively Registered October 8, 2018.