A new study is adding fuel to one of the biggest ongoing debates around cannabis—and it’s challenging a long-held assumption.
Researchers looking at regular cannabis users found no measurable cognitive impairment the next day, even when participants had used marijuana the night before. The study compared users to non-users roughly 12–15 hours after consumption and found no meaningful differences in performance across cognitive tests.
That finding lines up with a growing body of research suggesting cannabis doesn’t carry the same next-day “hangover effect” often associated with alcohol. In fact, researchers noted their results are consistent with prior reviews showing little evidence of lingering next-day impairment.
But here’s where it gets interesting: even without impairment, users can still test positive for THC long after the effects have worn off—sometimes days later in blood tests and even longer in urine.
That disconnect is exactly why groups like NORML say policies need to catch up with the science. Current workplace drug testing, they argue, often punishes people for past use rather than actual impairment in the moment.
The bigger takeaway? The science is starting to separate two things that have long been treated the same: being impaired vs. simply having used cannabis at some point in the past.
And as more data like this comes out, that distinction is becoming harder for regulators—and employers—to ignore.
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