Most people who use cannabis are familiar with the experience of feeling a bit foggy – misplacing a thought mid-sentence, forgetting what you walked into a room for, or struggling to follow a conversation. These moments are common, and they raise a fair question: what is cannabis actually doing to memory?
A new study from Washington State University has provided one of the most detailed answers yet. Published in the Journal of Psychopharmacology, the research mapped the effects of cannabis across 12 different types of memory – far more than most previous studies have examined – and found that the impact is broader than many people might expect.
What the researchers did
The study used a randomised, double-blind, placebo-controlled design – widely considered the gold standard in clinical research. One hundred and twenty cannabis-using participants were randomly assigned to vaporise cannabis flower containing either no THC (placebo), a moderate dose (20 mg THC), or a high dose (40 mg THC). Neither the participants nor the researchers administering the sessions knew which product was being used.
After vaporising, participants completed a battery of memory tests covering verbal memory, visuospatial memory (remembering images and spatial information), prospective memory (remembering to do something in the future), source memory (remembering where you learned something), false memory (susceptibility to remembering things that did not happen), and temporal order memory (remembering the sequence of events).
What they found
Compared with placebo, cannabis impaired performance across most of the memory domains tested. Specifically, participants who received THC showed reduced performance in immediate and delayed verbal memory, immediate and delayed visuospatial memory, verbal working memory, event-cued prospective memory, source memory, and temporal order memory. Cannabis also increased susceptibility to false memories – meaning participants were more likely to “remember” things that had not actually occurred.
Short-term verbal and visuospatial memory, time-cued prospective memory, and visuospatial working memory were not significantly affected.
One notable finding was that there were no significant differences between the moderate and high dose groups. Both doses produced similar levels of impairment across the affected domains.
Why this matters for everyday life
Previous cannabis research has focused heavily on verbal memory – the ability to remember words and language-based information. This study is among the first to detect acute effects on prospective memory and temporal order memory, which are types of memory that people rely on constantly in daily life.
Prospective memory is what allows a person to remember to pick up a prescription, call someone back, or take medication at a certain time. Temporal order memory helps with recalling the sequence of events – what happened first, what came next. Difficulties in these areas can affect work performance, relationships, and the ability to manage day-to-day responsibilities.
What this means if you are concerned
Experiencing memory difficulties related to cannabis use is not uncommon, and it does not mean something is permanently wrong. The effects examined in this study were acute – meaning they occurred while participants were under the influence, not weeks or months later.
At the same time, for people who use cannabis regularly, repeated acute impairment across this many memory domains may have a cumulative effect on how well they manage everyday tasks and responsibilities. Some people notice this pattern over time – feeling less organised, less reliable in their recall, or more frequently confused about details.
If cannabis use is affecting your memory, concentration, or ability to manage daily life, these are experiences that a qualified mental health professional can help with. A GP is often a good starting point – they can discuss your situation, assess whether a mental health care plan might be appropriate, and refer you to a psychologist or counsellor if needed.
You do not need to have a diagnosis or be in crisis to seek support. Many people find it helpful to talk through their concerns with a professional, particularly when substance use is involved.
Finding support
If you are thinking about speaking with someone, MentalHealth.net.au’s directory can help you find a qualified mental health professional in your area. You can search by location, specialty, and whether bulk-billing or Medicare rebates are available.
For immediate support, Lifeline (13 11 14) and Beyond Blue (1300 22 4636) are available 24/7.
This article is general information only and is not a substitute for professional medical advice. If you have concerns about cannabis use and your mental health, speak with a qualified health professional.
Sources:
Cuttler, C., & McLaughlin, R. J. (2026). Mapping the acute effects of cannabis on multiple memory domains: A randomized, double-blind, placebo-controlled study. Journal of Psychopharmacology. https://doi.org/10.1177/02698811261416079
