Ketamine-Assisted Therapy for PTSD: What Predicts Who Improves?

PTSD does not respond to treatment in everyone. Established therapies help a great many people, but a significant minority continue to struggle, and for them the search for something else is entirely reasonable. Ketamine, given at low doses under medical supervision, has become one of the more visible options, and clinics increasingly pair those sessions with psychotherapy.

That pairing raises an obvious question. When someone improves, what actually helped? The drug, the therapy, or the combination of the two? Individual studies have been too small and too different from one another to answer it.

A team led by Rohde, publishing in Psychotherapy and Psychosomatics (2026), found a way around that problem. Rather than comparing treatment groups in the usual way, they gathered the raw data on each individual patient from twelve separate studies, 533 people in total, and re-analysed it together. The approach is known as an individual participant data meta-analysis, and it allows questions the original studies were never designed to answer.

Four things predicted who improved.

The number of psychotherapy sessions someone received mattered. Each additional session was associated with roughly a further point of symptom reduction on a standard PTSD measure.

The number of ketamine sessions mattered too, although the authors describe that effect as more modest and less consistent. In a treatment named after the drug, the therapy dose was the steadier of the two signals.

Treatment duration ran in the opposite direction. The longer a course was spread out, the less people improved. Taken together with the session findings, that points towards intensity: more sessions delivered over a shorter period, rather than the same number stretched across months. It echoes what research into intensive trauma treatment has been showing for several years.

The strongest predictor of all was how severe someone's PTSD was at the outset. Those who began worse improved most, which is a pattern seen across trauma therapy generally.

The authors are careful about how far this should be taken. What counted as psychotherapy varied considerably between the studies, in content, in format and in how much trauma processing was involved. They describe their findings as hypothesis-generating rather than a basis for changing clinical guidelines.

One point is worth noting for readers here. EMDR was not among the therapies used in any of the twelve studies. This research says something genuinely interesting about combining ketamine with psychotherapy in general. It says nothing about combining it with EMDR in particular.

What it does suggest is that the therapy in these treatments is not incidental packaging around a drug. How much of it someone receives, and how closely together, appears to matter.

Source: Rohde, J., Moore, T. M., Walker, K., Ahmed, S. S., MacConnel, H. A., Krsak, M., Shannon, S., Tsang, V. W. L., Dames, S., Buchmann, M., Kleim, B., Seifritz, E., Olbrich, S., & Schoretsanitis, G. (2026). Ketamine-Assisted Psychotherapy for Posttraumatic Stress Disorder: A Systematic Review and Individual Participant Data Meta-Analysis of Predictors of Treatment Effects. Psychotherapy and Psychosomatics.