Cognitive Safety is Largely Ignored in Clinical Drug Trials: A Study of Registered Study Protocols

The number of reports on suspected drug-induced memory impairment submitted to the US Food and Drug Administration increased 30-fold from 2000 to 2022. Drugs are the most common cause of reversible dementia. However, there is very little research on drug-induced cognitive impairment. The aim of this study was to investigate if and how an assessment of cognitive safety was included in recent, registered, controlled, clinical drug trials.

The clinical trials registry ( www.

gov ) was searched for randomized controlled clinical trials with available study protocols. After excluding irrelevant trials such as surgical procedures, local or short-term treatment, and dietary supplements, 803 trials were included in this study. The protocols were manually reviewed for information on if, and how, cognitive safety had been assessed. Trial drugs were categorized into those targeting the central nervous system or not, as well as older and newer drugs. Methods used for the assessment of cognitive function were categorized into questionnaires, screening instruments, and neuropsychological tests. If the trial results were published, we examined whether the publication contained any data on cognitive safety that had emerged from the trial.

The start dates of the screened trials ranged from 31 July, 2009, to 4 April, 2021. Out of the 803 trials, 52 (6.5%) actively assessed cognitive safety. The remaining trials relied solely on spontaneous reporting. Of 429 trials studying a new drug, 32 (7.5%) actively assessed cognitive safety. One hundred and fifty-eight trials examined drugs intended to, or known to have, pharmacological effects on the central nervous system. Of these, 21 (13.5%) assessed cognitive safety. Most of the trials that assessed cognitive safety used either crude screening tools or questionnaires.

Cognitive safety is largely ignored by recent controlled clinical trials. This applies even to trials assessing new drugs and trials assessing central nervous system drugs. There is an urgent need for drug manufacturers, regulatory authorities, and the medical profession to address the cognitive safety of drugs.