Contents
The meta-analyses agree that mental health chatbots reduce symptoms of depression and anxiety. The effect size is around 0.3, which in this literature is modest but real. The problem lies in what emerges when you read the trials one by one. In the trial that compared a purpose-built therapy app against plain ChatGPT, the app did not outperform the generic chatbot on any measure. In the one that followed 540 people for six weeks, the AI version multiplied usage frequency by 2.4 and time spent by 3.8, and symptoms improved just as much as with static workbooks. And in the meta-analysis with three-month follow-up, the effect had disappeared. This article walks through the five measurements.
The 30-second summary: the seven figures that matter
Each row names the study and the year. Always look at what the chatbot is being compared against.
| Finding | Result | Study and year |
|---|---|---|
| Effect on depression across 38 randomised trials | g = 0.31 (95% CI: 0.17-0.46), with 7,401 participants | Sohn et al., NPJ Digital Medicine (2026) |
| Effect on anxiety across 34 of those trials | g = 0.28 (95% CI: 0.05-0.51) | Sohn et al., NPJ Digital Medicine (2026) |
| Effect at three-month follow-up | No substantial effects on depression or anxiety | Zhong et al., J. Affect. Disord. (2024) |
| Therapy app against generic ChatGPT | No differences on any measure | Kuta et al., JMIR Mental Health (2025) |
| Use of an AI app against workbooks | 2.4 times the frequency and 3.8 times the duration | McFadyen et al., Comm. Medicine (2026) |
| Symptoms in that same comparison | Comparable: no added improvement in anxiety or depression | McFadyen et al., Comm. Medicine (2026) |
| Comparator in the most-cited trial | A waiting list with no access to any app | Heinz et al., NEJM AI (2025) |
What you will find here
• How much these systems reduce symptoms, according to the synthesis of 39 trials.
• The trial where the therapy chatbot drew level with plain ChatGPT.
• Why multiplying usage fourfold did not improve symptoms.
• What happened when measured three months after the end.
The magnitude of the impact
The most recent and comprehensive synthesis was published by Jun-Seok Sohn and colleagues in NPJ Digital Medicine in 2026, searching five databases from 2017 with prior PROSPERO registration. Out of 39 eligible randomised trials, depression was evaluated in 38 studies involving 7,401 participants, whereas anxiety was assessed in 34 trials comprising 7,621 individuals.
The pooled results: a statistically significant reduction in depressive symptoms, with g = 0.31 (95% CI: 0.17-0.46), and in anxiety symptoms, with g = 0.28 (95% CI: 0.05-0.51). On the usual scale, these are small effects.
There exists a helpful nuance within the subgroup analysis: the impact on depression proved greater among clinical and subclinical cohorts relative to non-clinical groups (p = 0.001). In other words, these interventions perform more effectively for individuals experiencing greater distress, which represents the preferred trajectory.
What that figure does not distinguish
An effect of 0.3 against a group receiving nothing is not the same as an effect of 0.3 against a reasonable alternative. Many of these trials compare the chatbot with a waiting list, that is, with doing nothing, and in mental health that systematically inflates the result through expectation, attention and the simple passage of time.
| Study | What it compared against | What it found | What it cannot support |
|---|---|---|---|
| Heinz et al., NEJM AI (2025) | Waiting list, with 210 adults over 4 weeks | The reference trial of an expert-fine-tuned chatbot | Without an active comparator, it cannot isolate the effect of receiving something |
| Kuta et al., JMIR Mental Health (2025) | Generic ChatGPT and a no-intervention group, 185 adults | Both reduce depression; between them, no difference | Small sample and a three-week intervention |
| McFadyen et al., Comm. Medicine (2026) | Digital cognitive behavioural therapy workbooks, 540 adults | Far more use, the same symptoms | Self-guided and unblinded |
| Sohn et al., NPJ Digital Medicine (2026) | Synthesis of 39 trials with any control | g = 0.31 on depression and 0.28 on anxiety | It pools very different comparators |
| Zhong et al., J. Affect. Disord. (2024) | 18 trials with 3,477 participants | Improvements at eight weeks and nothing at three months | Heterogeneous designs and therapeutic approaches |
The trial that compared against plain ChatGPT
This is the research that ought to be shared most widely yet travels the least. In 2025, Barbora Kuta along with her colleagues published a trial in JMIR Mental Health featuring 185 adults split into three groups: a generative therapy app based on solution-focused therapy, general-purpose ChatGPT, and a no-intervention control group. Three weeks, with nine scheduled sessions per active cohort.
Compared to the control cohort, both active arms showed reductions in depressive symptoms according to the PHQ-9 inventory: d = −0.47 (p = 0.01) within the AI therapy cohort alongside d = −0.44 (p = 0.02) inside the ChatGPT cohort. Regarding anxiety levels and overall wellbeing, neither arm achieved statistical significance.
And the conclusive outcome: the therapy app group failed to surpass the ChatGPT group across every single metric. Discrepancies between them proved negligible and statistically insignificant regarding depression, anxiety, and overall wellbeing.
A small three-week trial should not be over-interpreted. But it does raise an uncomfortable question for the whole sector: if a tool designed specifically to do therapy cannot be told apart from a general-purpose chatbot, what is working may not be the therapeutic design.
Far more use, the same symptoms
The trial by Jessica McFadyen and colleagues, published in Communications Medicine in 2026, is the largest of the individual studies: 540 adults in the United States with elevated symptoms of anxiety or depression, preregistered, split between a cognitive behavioural therapy app powered by generative AI and digital workbooks of the same therapy, self-guided over six weeks.
| What was measured | AI app | Digital workbooks |
|---|---|---|
| Usage frequency | 2.4 times higher | Baseline |
| Usage duration | 3.8 times higher | Baseline |
| Anxiety symptoms (GAD-7) | Comparable | Comparable |
| Depression symptoms (PHQ-9) | Comparable | Comparable |
| Adverse events | No differences | No differences |
The authors’ conclusion is honest and applies across the field: in self-directed use, tailored generative-AI-enabled therapy safely enhances user engagement above and beyond static materials, without showing an overall enhancement in anxiety or depression symptom reduction.
Put another way: AI solves the problem of people abandoning these tools, which is real and important, and not the problem of making them work better. An exploratory analysis in the same work suggests that those who used the clinical personalisation features did see greater anxiety reduction, but that is a comparison between people who chose to use them, not a random assignment.
What is left three months later
Wei Zhong, Jiang-Hua Luo and Hong Zhang published a meta-analysis in the Journal of Affective Disorders in 2024 covering 18 randomised trials with 3,477 participants, searching five databases.
Their immediate results are consistent with the rest: improvements in depression (g = −0.26; 95% CI: −0.34 to −0.17) and anxiety (g = −0.19; 95% CI: −0.29 to −0.09), with maximum benefit after eight weeks of treatment.
And the figure that almost never makes the headlines: at three-month follow-up, no substantial effects were detected for either condition. The benefit exists while use continues and does not appear to leave anything behind.
That limitation connects with a detail of the field’s reference trial, by Michael Heinz and colleagues in NEJM AI in 2025, which tested an expert-fine-tuned generative chatbot with 210 adults with clinically significant symptoms of major depression, generalised anxiety or high risk for an eating disorder. The comparison group was a waiting list with no access to any app during the study’s four weeks. It is the design that most inflates any effect, and it underpins much of the public conversation on the subject.
Practical ways to handle this
Ranked by the robustness of its supporting data:
• Ask what it was compared against before believing a figure. A waiting list is not an active comparator, and many of these trials use one.
• Do not expect the effect to last. The meta-analysis with three-month follow-up found no substantial effects on depression or anxiety.
- When retention is the primary objective, artificial intelligence certainly delivers results. Compared to conventional static content, it boosted engagement frequency by 2.4 times and extended session lengths by a factor of 3.8.
• Do not assume a specialised tool is better. In the only trial that compared them, it did not outperform generic ChatGPT on any measure.
- Consider it an adjunct for mild or moderate situations. The combined effect, g = 0.31, is modest yet significant, displaying greater magnitude among clinical groups than within the broader community.
Frequently asked questions
Do therapy chatbots work?
They have a real, small effect. The meta-analysis of 39 randomised trials published in NPJ Digital Medicine in 2026 estimates a reduction in depressive symptoms of g = 0.31 (95% CI: 0.17-0.46) with 7,401 participants, and in anxiety symptoms of g = 0.28 (95% CI: 0.05-0.51), with larger effects in clinical and subclinical samples than in the general population.
Does the improvement hold over time?
The available evidence says no. The meta-analysis of 18 trials with 3,477 participants found improvements in depression (g = −0.26) and anxiety (g = −0.19), peaking at eight weeks, but detected no substantial effects at three-month follow-up.
Does a therapy app surpass using ChatGPT directly?
In the only trial to have compared them, no. With 185 adults split between a generative therapy app, general-purpose ChatGPT and a control group, both active groups reduced depression against the control (d = −0.47 and d = −0.44), and the specialised app did not outperform ChatGPT on any measure. It is a small, three-week study.
What is AI actually for in these apps?
Above all, when it comes to encouraging adoption. During the study involving 540 subjects, the generative-AI variant boosted usage frequency by a factor of 2.4 and session length by 3.8 relative to conventional digital workbooks addressing the same therapy, yielding similar outcomes for anxiety and depression alongside identical adverse event rates. High attrition plagues digital interventions, and this is precisely where the solution proves beneficial.
Why does the comparison group matter so much?
Because it changes the reading of the result entirely. The field’s most-cited trial, published in NEJM AI in 2025 with 210 adults with clinically significant symptoms, compared the chatbot with a waiting list that had no access to any app. Against receiving nothing, almost any intervention improves measured symptoms.
What we do not know
• How they compare with human therapy. None of these trials contrasts the chatbot with equivalent face-to-face psychotherapy.
• What happens in a crisis. Trials usually exclude people at acute risk, who are precisely the greatest concern.
- Whether the impact stems from the material or the interaction itself. The appeal seen with a standard chatbot implies that therapeutic structuring might not be the defining element.
• Almost nothing in adolescents and older adults. The 2026 review explicitly notes the absence of studies in those two age groups.
References
1. Sohn, J.-S., Ha, B.-G. et al. Systematic review and meta analysis of chatbots in the management of depressive and anxiety symptoms. NPJ Digital Medicine, 2026. DOI: 10.1038/s41746-026-02566-w
2. Kuta, B., Novak, L. et al. Effectiveness of a Fully Automated Mobile Therapeutic Versus a General Chatbot in Reducing Depression and Anxiety and Improving Well-Being. JMIR Mental Health, 2025. DOI: 10.2196/82642
3. McFadyen, J., Habicht, J. et al. Increasing engagement with cognitive-behavioral therapy (CBT) using generative AI: a randomized controlled trial. Communications Medicine, 2026. DOI: 10.1038/s43856-025-01321-8
4. Zhong, W., Luo, J.-H. and Zhang, H. The therapeutic effectiveness of artificial intelligence-based chatbots in alleviation of depressive and anxiety symptoms in short-course treatments. Journal of Affective Disorders, 2024. DOI: 10.1016/j.jad.2024.04.057
5. Heinz, M. V., Mackin, D. M. et al. Randomized Trial of a Generative AI Chatbot for Mental Health Treatment. NEJM AI, 2025. DOI: 10.1056/aioa2400802
This content is for information only and does not constitute medical or psychological advice, nor does it replace care from a mental health professional. If you are in a situation of risk, contact your local emergency services or helpline.
