Evidence accumulated quickly, especially after 2020. Meta-analyses of cognitive behavioural therapy delivered online consistently find effects comparable to the in-person format for depression and anxiety disorders, including at long-term follow-up. The therapeutic alliance — the supposed great casualty of the screen — forms at similar levels.
Where online has a practical advantage: access to a specialised therapist who is not in your city, no journey, continuity while travelling, and a lower entry threshold for anyone who would otherwise put it off for months.
Where the physical format has arguments: in severe trauma work, where regulation in the room matters; where there is active suicide risk, which needs a setting with clear procedures; and where there is no space at home in which you can speak freely — which is the most frequent real obstacle, far more than the technology.
What matters practically for an online session: headphones, a place nobody can walk into, a plan agreed in advance for the connection dropping, and the camera on — an audio-only session loses facial expression, which is information for both of you.
Online couples therapy works, but it needs both partners in the same room or, failing that, each with their own device and their own headphones.