Any person sufficiently deprived of sleep may experience hallucinations while awake; a small amount of coffee or tea before sleep aids dream recall, while substances that suppress activity inhibit dreaming.

Caffeine: approximately 120 participants, doses 0, 25, 50 mg before sleep, randomized double-blind crossover, 2 nights per condition with adequate washout between conditions, personal period 6–8 weeks; use identical decaffeinated beverage plus blind capsules, controlling for habitual intake, withdrawal, pre-sleep sleepiness, and sleep schedule. Awaken during matched REM cycles and matched continuous REM durations after polysomnography; primary outcome is dream recall rate per effective REM awakening, secondary outcomes are report length, information units, and morning dream recall; no REM cannot count as no dream. Alcohol: independent approximately 100 participants, crossover with placebo drink and low-dose ethanol (~0.2 g/kg), each condition with a natural sleep night and a standardized awakening night, personal period 4–6 weeks; measure blood or breath alcohol, REM proportion, microarousals, and post-awakening memory; evaluate blinding success. Use preregistered mediation analyses to separate effects via sleep structure from residual effects, but adjusting for REM as a post-treatment variable cannot automatically identify direct causal action. Hypnotics must be studied one by one and cannot be pooled as "activity-suppressing substances." For hallucinations, prioritize reanalysis of existing sleep-deprivation data and natural-exposure cohorts, about 1000 participants, 12 months; no extreme deprivation is arranged to validate any person.

Low-Dose Caffeine and Alcohol Effects on REM Dream Recall: Randomized Crossover Studies With Polysomnographic Mediation Analysis

If drugs alter dream recall after matching sleep stage and awakening opportunity, this would refute the simple hypothesis that dream-recall changes are entirely explained by REM duration and awakening opportunity.

Carissa Gardiner; Shona L. Halson — Australian Catholic University; Perrine M. Ruby — Lyon Neuroscience Research Center; Francesca Siclari — Netherlands Institute for Neuroscience; Flavie Waters

Small pre-sleep doses and enhanced dream recall constitute distinguishable directional predictions, but "small" is not quantitative, and coffee/tea are not pure caffeine; "any person" and "all suppressing substances" are overgeneralizations unsupported by evidence.

The composite item cannot be uniformly judged as supported: sleep deprivation causing hallucinations has support; small-dose caffeine or alcohol enhancing dream recall was not directly confirmed in this search; the claim that sedative substances universally suppress dreaming is too strong; existing teams conduct pharmacological modulation, 256-channel EEG, and serial awakenings research.[Related project](https://nin.nl/internships/pharmacological-modulation-of-dreaming/)