Whether the Ketamine Experience Matters Depends on Which Questionnaire You Use
Does the experience during a ketamine session matter to the result? A letter published this week in npj Mental Health Research argues the answer depends on which questionnaire researchers hand the patient. Using the same ketamine studies, one scale explains about 3 percent of the outcome. Another explains about 15 percent.
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| Key Takeaway | Detail |
|---|---|
| The letter | A Matters Arising critique of a 2024 meta-analysis, published September 22, 2026 |
| The original finding | Subjective effects explained 5 to 10 percent of ketamine outcomes and 24 percent for psilocybin |
| The objection | The two drugs were measured with different instruments, so the comparison is not like for like |
| The number | Across ketamine studies, CADSS explained 3.3 percent and BPRS explained 15 percent |
| The agreement | Both sides find a much stronger link in addiction studies than in depression studies |
| The caveat | This is one author’s letter, not new patient data |
What the 2024 Analysis Concluded
Jack Dahan and colleagues pooled studies that correlated subjective effects with clinical improvement. They published it in npj Mental Health Research in October 2024.
They retrieved 23 ketamine papers covering 471 patients and 8 psilocybin papers covering 183 patients. Subjective effects explained roughly 5 to 10 percent of the outcome for ketamine.
For psilocybin the figure was 24 percent. The authors concluded that the experience plays a modest role, and a larger one for psilocybin than for ketamine.
The Objection
Ramūnas Janavičius, a clinician in Vilnius, argues the two halves were never measured the same way.
Ketamine studies mostly used the CADSS, a dissociation scale, or the BPRS, a general psychiatric symptom scale. Psilocybin studies used mystical experience questionnaires built for psychedelic states.
Those instruments capture different things. A scale designed to detect mystical experience will track a mystical experience more closely than a scale designed to detect dissociation.
The Number That Makes the Case
The strongest part of the letter compares studies inside the ketamine group alone. The drug is held constant. Only the questionnaire changes.
Six studies using CADSS pooled to a correlation that explains about 3.3 percent of the variance in outcome. Four studies using BPRS explain about 15 percent.
Two ketamine studies in substance use disorder used a mystical experience scale instead. Those explained about 54 percent, close to the 60 percent reported on the psilocybin side.
Where Both Sides Already Agree
The original analysis found its own large signal in addiction. Its two ketamine studies in alcohol and cocaine use disorder pooled far higher than the depression studies.
So both the paper and its critic point at the same pattern. The experience looks more important in addiction treatment than in depression treatment.
We have covered evidence running the other way too. One analysis suggested ketamine’s psychedelic effects may not be why it helps alcohol addiction. Ibogaine work found mystical experiences linked to greater PTSD relief.
The Therapy Problem
The letter raises a second issue. Every psilocybin study in the analysis included psychotherapy. The ketamine studies were selected to exclude it.
That means the psilocybin side bundled drug and therapy together, and the ketamine side did not. Whether therapy explains the gap is unsettled. Our look at the evidence for ketamine assisted psychotherapy covers what is known.
What It Means Inside a Clinic
Many practices already score the CADSS during monitoring. It is the standard tool for tracking dissociation in a Spravato or infusion workflow.
That is a safety and monitoring instrument. This letter argues it is also the weakest of the available tools for answering whether the experience contributed to the result.
A clinic that wants its own answer would need to add a second measure of the experience alongside the CADSS. That is a research decision, not a standard of care, and it carries staff time.
It is worth knowing before a practice concludes anything from its own numbers. A recent trial found higher dissociation scores tracked better esketamine outcomes, and it used the CADSS.
How Much Weight to Give It
This is a single-author letter, not new patient data. It reanalyzes numbers already published by someone else, and the original authors may respond.
The author acknowledges Rick Doblin of MAPS for encouragement. MAPS has long argued that the experience is central to the treatment.
The underlying question also remains hard to settle. Patients usually know whether they received an active drug. We covered that problem when FDA confronted blinding in psychedelic trials.
The Bottom Line
Nobody has shown that the experience causes the benefit. This letter does show that the measurement choice moves the estimate by a factor of four or five.
That is a reason to treat confident claims in either direction with suspicion. It is also a reason for future trials to use the same instruments across drugs.
Patients looking for supervised care can start with our directory of verified ketamine clinics.
This article is for informational purposes and is not medical advice. It describes a methodological debate in published research and does not change current treatment practice.
