What the experiment tested
Twelve regular cannabis smokers took part in placebo and active-cannabis weekends. The active condition used 2.1% THC cannabis, with 40 standardized puffs across five smoking periods. The following mornings, researchers assessed subjective effects, mood and performance. Most measures showed no meaningful residual effect; the author did not find an alcohol-like hangover pattern. Original study.
Why that conclusion is narrow
The small sample, regular users and specific smoking protocol limit generalization. A negative result under those conditions does not prove that modern high-dose products, edibles or every individual are free of next-day effects. This experiment also does not establish a universal time after consumption when driving is safe.
Read the original research
Subjective and behavioral effects of marijuana the morning after smoking.
Psychopharmacology
Citation
L D Chait. (1990). Subjective and behavioral effects of marijuana the morning after smoking.. Psychopharmacology. https://doi.org/10.1007/BF02244601