Readability of informed consent forms from ClinicalTrials.gov in ketamine clinical trials for mental health conditions: a cross-sectional analysis.
Damian Swieczkowski, Aleksander Kwaśny, Wiesław Jerzy Cubała
Therapeutic Advances in Psychopharmacology June 29, 2026 DOI: 10.1177/20451253261456385 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Cross-sectional analysis Peer reviewed |
|---|---|
| Sample size | 14 |
| Population | English-language informed consent forms from interventional ketamine clinical trials for mental health conditions posted on ClinicalTrials.gov |
| Measures | Flesch-Kincaid Grade Level, Gunning Fog Index, Flesch Reading Ease Score, Fry Readability Graph |
| Topics | Esketamine Ketamine |
| Keywords | Psychiatric disorders Health literacy Informed consent forms Readability assessment Ketamine clinical trials |
| Key findings | Thirteen of 14 ketamine mental health trial consent forms exceeded recommended readability thresholds, with a mean Flesch-Kincaid Grade Level of 9.8 and a mean estimated silent reading time of 21.4 minutes. The authors argue sponsors and ethics committees should require consent materials to meet an eighth-grade reading level, verified by a documented readability assessment before approval. |
Abstract
Background: Ensuring participants understand informed consent forms (ICFs) is a core ethical requirement of clinical research, particularly in psychiatry, where cognitive and affective symptoms can compromise decisional capacity. As ketamine-based interventions are increasingly studied for mental health conditions, the readability of consent materials in these trials warrants systematic evaluation.
Objectives: To assess the readability and linguistic complexity of ICFs from ClinicalTrials.gov used in ketamine clinical trials for mental health conditions.
Design: Cross-sectional analysis.
Methods: We conducted a cross-sectional analysis of English-language ICFs posted on ClinicalTrials.gov for interventional ketamine clinical trials involving mental health conditions. All documents were converted to plain text and standardised for text-based analysis. Readability and linguistic complexity were assessed using established indices, including the Flesch-Kincaid Grade Level, Gunning Fog Index, Flesch Reading Ease Score, and Fry Readability Graph. Document length and estimated silent reading time were also calculated. Descriptive statistics summarised the findings.
Results: Fourteen ketamine clinical trials met the inclusion criteria. ICFs ranged from 1681 to 8637 words (mean: 5031; median: 4622), with sentence counts from 129 to 503. Estimated silent reading times ranged from 7.0 to 36.0 min (mean: 21.4; median: 19.5). Flesch-Kincaid Grade Level scores ranged from 5.7 to 11.5 (mean: 9.8), with 13 of 14 documents above grade 8. Gunning Fog Index values ranged from 7.7 to 13.8 (mean: 11.7). Flesch Reading Ease Scores ranged from 41.3 to 73.9 (mean: 52.8). Fry Readability scores ranged from grade 6 to grade 13.
Conclusion: Thirteen of fourteen ketamine mental health trial consent forms on ClinicalTrials.gov exceeded recommended readability thresholds. Sponsors and ethics committees should require consent materials to meet an eighth-grade reading level, verified by a documented readability assessment before approval, to support informed participation in psychiatric research.
Comparable studies
Other cross-sectional and survey studies on ketamine, most cited first.
| Study | Year | Design | Participants |
|---|---|---|---|
| 5-Year Trends in Use of Hallucinogens and Other Adjunct Drugs among UK Dance Drug Users People who use drugs in dance contexts | 2006 | Repeated-measures cross-sectional survey | |
| Preliminary analysis of positive and negative syndrome scale in ketamine-associated psychosis in comparison with schizophrenia Healthy subjects, ketamine abusers, and schizophrenia patients | 2014 | Cross-sectional study | n = 998 |
| Ketamine as a primary predictor of out-of-body experiences associated with multiple substance use Online survey respondents | 2011 | Cross-sectional survey | n = 192 |
| Self-reported prevalence of dependence of MDMA compared to cocaine, mephedrone and ketamine among a sample of recreational poly-drug users Global non-treatment-seeking sample of last year users of MDMA, cocaine, mephedrone,... | 2014 | Cross-sectional survey | |
| Near-Death States Reported in a Sample of 50 Misusers Previous ketamine misusers who reported a ketamine-related near-death experience | 2010 | Cross-sectional survey | n = 50 |