While hazy memories are a common side effect of smoking cannabis, a new study has suggested that it can make those memories feel real when they're actually not.
Even though cannabis remains illegal and a Class B drug in the UK, according to data from the Crime Survey for England and Wales, it has been the most commonly used illicit substance in England and Wales every year since records began in 1995.
Researchers at Washington State University recruited 120 cannabis users and randomly assigned them to inhale either real cannabis containing 20 or 40 milligrams of THC - the main psychoactive compound in cannabis - or a placebo.
Participants then completed 21 different memory tests, many of which had never before been used in cannabis research.
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The results showed 70 percent of the participants had some level of memory impairment after consuming THC.
And the worst side effect was false memory and recalling events or details that never happened.
Why do these 'false memories' happen?
Scientists think false memories happen when the brain tries to reconstruct incomplete information.
Because THC weakens the recollection but leaves the general sense of familiarity intact, people may feel certain about memories that are inaccurate.
"Relative to placebo, cannabis increased susceptibility to false memories and detrimentally impacted verbal memory (immediate, delayed, working), visuospatial memory (immediate, delayed), event-cued prospective memory, source memory, and temporal order memory," the researchers wrote.
"There were no significant differences between the moderate and high dose groups."
Carrie Cuttler, an associate professor and co-author of the 2026 study, told National Geographic: "You are activating certain pathways to create a memory and to recall something, you are trying to reactivate that same pathway."
"If you blast the system with THC, the THC hijacks the system," she explained.
Authors said it was 'the first study to detect acute effects of cannabis on prospective memory and temporal order memory, which is important because these tests better reflect everyday memory and predict daily functioning'.
"Collectively, these results indicate that acute cannabis use has broad detrimental effects on most domains of memory rather than selectively impairing a limited number of these domains," they added.
Cuttler, however, notes that the side effect isn't likely to impact you in the same way alcohol does and can.
“Acute alcohol intoxication is generally more disruptive to memory than cannabis," said Cuttler.
She explained that THC side effects can also dramatically reduce after 'a person abstains from cannabis for a month'.
Common side effects from smoking weed
According to Mayo Clinic, other common side effects from marijuana use include:
- Altered senses, like seeing brighter colors or smelling scents more intensely
- Altered sense of time and space
- Euphoria and mood changes
- Issues with thinking and problem-solving
- Impaired memory
- Disorientation and confusion
- Relaxation and/or sleepiness (sedation)
- Dizziness
- Issues with coordination
- Slowed reaction time
- Experiencing a panic attack
Anish Vij