What Is the CADSS Dissociative Scale? Definition Explained

The CADSS, short for Clinician-Administered Dissociative States Scale, is a standardized questionnaire used to measure how intensely a person is experiencing dissociation, such as feeling detached from their body, their surroundings, or their sense of time, at a specific moment. It is the most widely used rating tool in ketamine and esketamine research for tracking the acute psychoactive effects that occur during and shortly after dosing.

You will not typically fill out a CADSS as a patient in a routine ketamine clinic visit. It is primarily a clinical trial and research instrument, though some Spravato (esketamine) treatment centers use it or similar monitoring checklists as part of required post-dose safety observation.

Where the CADSS Came From

Psychiatrist J. Douglas Bremner and colleagues developed the CADSS in the late 1990s to measure dissociative symptoms in people with post-traumatic stress disorder (PTSD) and other trauma-related conditions, publishing the validation study in the Journal of Traumatic Stress in 1998. The scale was built to capture state dissociation, meaning symptoms happening right now, rather than a person's general trait tendency toward dissociation.

Ketamine researchers adopted the CADSS starting in the early 2000s because ketamine reliably produces transient dissociative effects at subanesthetic doses, and investigators needed a consistent way to quantify that response across studies. You can read more background on what this experience involves in our ketamine dissociation meaning glossary entry.

What the Scale Actually Measures

The CADSS contains 23 items grouped into three general domains that overlap with how clinicians describe dissociation:

• Derealization: the surroundings feel unreal, dreamlike, or altered
• Depersonalization: the self or body feels detached, unfamiliar, or observed from outside
• Amnesia: gaps or fuzziness in memory for the period being rated

Most versions include both a clinician-rated set of items, scored by an observer watching the patient's behavior and responses, and a subject-rated set completed by the patient describing their own internal experience. Each item uses a 0-to-4 severity scale, and the items are summed into a total score, so a higher number reflects more intense dissociation at that specific time point rather than a diagnosis or a fixed clinical category.

How CADSS Is Used in Ketamine and Esketamine Research

In a typical ketamine or esketamine study, staff administer the CADSS at baseline, before any drug is given, and then again at set intervals afterward, often around 40 minutes and again at 2 to 4 hours post-dose, to chart how dissociation rises during the acute drug effect and resolves as the medication clears. This mirrors what happens with ketamine's metabolites in the body, since dissociative intensity generally tracks with plasma drug levels rather than persisting long after infusion or dosing ends.

Researchers use CADSS scores for a few distinct purposes. They help confirm that a dose is reaching an active, psychoactive range, they let trial teams compare dissociation intensity across routes of administration such as intravenous (IV) infusion, intramuscular (IM) injection, or intranasal esketamine, and they give safety monitors an objective marker to follow during required observation periods. Studies comparing routes, such as research on IV ketamine versus nasal esketamine, frequently report CADSS scores as a secondary outcome alongside depression rating scales.

The relationship between CADSS scores and antidepressant response is an active research question, not a settled fact. Some studies have reported a correlation between higher acute dissociation and better short-term mood improvement, while others have found no significant relationship once other variables are controlled for. The evidence is mixed enough that a clinician should not use a person's CADSS score alone to predict how well ketamine will work for them. If you want a primer on evaluating this kind of research, see our guide on how to read ketamine depression research studies.

How to Interpret a CADSS Score

There is no single universal cutoff that defines a "high" or "low" CADSS score across all studies, because research teams sometimes use the full 23-item version, a shortened version, or slightly different scoring conventions. What matters for interpretation is the pattern: scores that rise sharply during the drug's peak effect and return toward baseline as the dose wears off are the expected pattern for ketamine's mechanism, which involves rapid absorption and distribution depending on route and a relatively short half-life. A score that stays elevated well past the expected pharmacological window, or that is paired with distress the person cannot tolerate, is a signal for the treatment team to reassess rather than a number with a fixed clinical meaning on its own.

It's also useful to distinguish CADSS-rated dissociation from an emergence reaction, which refers specifically to confusion, agitation, or vivid unpleasant sensations as a person comes out of a ketamine dose, since the two are related but not identical concepts in the research literature.