As cannabis gains legal ground around the world, its cultural and medical revival has been celebrated far and wide. Yet, amid this green renaissance, one pressing question often goes unasked: What happens to memory under the influence of cannabis?
In a world increasingly reliant on eyewitness testimonies, especially in legal proceedings, the reliability of memory becomes a matter of justice. Enter Kloft et al. (2020) — a landmark study probing how cannabis might shape, twist, or even invent our recollections. This blog post unpacks their research, revealing how THC intoxication doesn’t just dull memory — it warps it, increasing the risk of false memories in real-world scenarios.
Buckle up for a trip into the mind under the influence — where memory becomes a murky mix of fact and fiction. 
1. The Scientific and Legal Context
Cannabis is the world’s most popular illicit drug, with usage skyrocketing amid changing laws and social attitudes. Yet, cannabis is not just a buzz — it directly interacts with brain systems tied to memory and cognition.
Why does this matter? In legal cases, especially those involving assault, theft, or other criminal activity, eyewitness testimony can often be the only available evidence. But if that testimony is tainted — not by malice, but by altered memory — the consequences can be devastating: wrongful convictions, false accusations, and miscarriages of justice.
That’s where this study steps in: to rigorously test how THC, the psychoactive compound in cannabis, affects the formation and recall of false memories.
2. Study Design: Science at Its Best
This wasn’t a casual survey or anecdotal collection. It was a randomized, double-blind, placebo-controlled clinical trial, the gold standard of experimental design.
Researchers recruited 64 healthy, occasional cannabis users, and each participant underwent two conditions:
• Cannabis condition: They inhaled a THC dose proportional to their body weight.
• Placebo condition: They inhaled a non-psychoactive substitute.
Participants completed two memory tests in both conditions:
• Immediately after exposure (while still intoxicated)
• One week later (completely sober)
This design allowed the researchers to differentiate acute effects (under the influence) from residual effects (lasting memory distortions).
Memory was tested using three powerful paradigms:
1. DRM Paradigm (Spontaneous False Memories) – where people falsely “remember” words that were never shown but are semantically related.
2. VR Eyewitness Scenario (Misinformation-based) – participants watched a VR crime scene, then were questioned.
3. VR Perpetrator Scenario (Misinformation-based) – participants enacted a VR theft and were later quizzed on details.
These methods combine lab precision with real-world relevance, making this one of the most comprehensive studies of cannabis and memory to date.
3. False Memories: What Are They Really?
Before diving into the results, let’s clarify what “false memory” means. It’s not lying or deliberately misremembering. A false memory is a genuine belief in something that never happened.
Two main types were studied:
• Spontaneous False Memories: Internal errors caused by mental associations.
• Suggestion-Based False Memories: External influence from misleading information (e.g., “Was the thief wearing a red hat?” when there was no hat at all).
Cannabis, by altering neural signaling — especially in the hippocampus, a key memory hub rich in CB1 receptors — may affect both types.
4. Key Finding 1: Cannabis Promotes Spontaneous False Memories
Using the DRM paradigm, participants were shown lists of related words (e.g., “bed,” “tired,” “dream”) but not the critical lure (“sleep”). Later, they were asked to recognize which words they’d seen.
Results:
• Cannabis users falsely recognized more related and unrelated words, especially when still intoxicated.
• Surprisingly, their true memory (recognizing actual words) wasn’t significantly impaired immediately — they were just more likely to say “yes” to new but similar words.
• After a week, some false memories persisted, suggesting that THC affected encoding as well as retrieval.
Interpretation: Cannabis intoxication fosters a “yes bias” — people become more likely to affirm they saw or remember something, especially when it’s loosely associated with actual experiences.
5. Key Finding 2: Cannabis Makes You a Riskier Witness
In the eyewitness VR scenario, participants watched a simulated fight at a train station, then were exposed to misinformation via a co-witness and interview questions.
Results:
• Cannabis-intoxicated participants had higher false memory rates for:
• Suggested details (misleading questions)
• Non-suggested, non-presented details (pure invention)
• After one week, the differences disappeared — acute intoxication was the key risk window.
Takeaway: Cannabis impairs a person’s ability to resist suggestion and discern what actually happened, especially soon after an event. In legal contexts, this is critical.
6. Key Finding 3: False Confessions from the Perpetrator’s Chair?
In the perpetrator VR scenario, participants played the role of a thief stealing a handbag. Later, they were asked about their own actions and the setting.
Results:
• Intoxicated participants again showed higher false-memory rates, particularly for non-suggested details.
• These were not details they were prompted about — participants fabricated them based on faulty memory.
• Again, these effects vanished after a week, confirming the acute nature of the impairment.
This suggests that suspects under the influence of cannabis might unintentionally incriminate themselves or others, not out of guilt — but due to memory distortions.
7. Yes Bias and Source Confusion: Why It Happens
Why does cannabis increase false memories? Several mechanisms are likely at play:
• CB1 Receptor Activity in the Hippocampus: This facilitates incidental associations, making users more likely to form irrelevant mental links.
• Source Monitoring Deficits: Cannabis users may confuse internal thoughts or external suggestions with actual memories.
• Weakened Discrepancy Detection: Users are less likely to spot contradictions in misleading narratives.
Together, these changes produce a mind more open to fabricated recollections, and more confident in inaccurate memories.
8. Science Meets the Courtroom: Implications for Law Enforcement
The practical implications are profound. Cannabis users are often involved in legal investigations — as witnesses, victims, or suspects. If THC increases the risk of false memories:
• Interviewing intoxicated individuals should be delayed until they’re sober.
• Cannabis-intoxicated individuals might need to be treated as a vulnerable group, akin to children or the elderly.
• Standard drug testing should be considered not just for suspects, but for witnesses, especially when memory is the primary evidence.
• Legal professionals must be trained in memory reliability and cognitive bias, particularly in drug-affected individuals.
9. The Long-Term View: Is It Just a Phase?
While most cannabis-induced memory distortions occurred during the acute phase, some subtle effects lingered a week later — particularly in spontaneous memory tasks.
• This suggests THC may impair encoding, not just recall.
• Impaired encoding means that even when sober, a person may have faulty memories formed under the influence.
Thus, even if a person is sober during an interview, if they were intoxicated during the event, their memory may already be compromised.
10. Limitations and What’s Next
The study was robust but not without limitations:
• It used recognition memory; future research should include free recall and confidence judgments.
• Effects in chronic users or those with comorbidities remain unclear.
• Would cannabis-intoxicated people make more false accusations or be more suggestible in real-world interviews?
Future directions might include:
• Longer-term studies on memory decay post-cannabis use.
• Neuroimaging research to pinpoint exact brain activity changes.
• Studies on metacognition: Do users realize they’re more prone to memory errors?
Cannabis, Memory, and the Fragile Truth
Kloft et al. (2020) shine a spotlight on a little-discussed effect of cannabis — not on attention or reaction time, but on truth itself. In a world where the line between real and remembered is already blurry, THC adds another smudge.
Cannabis can heighten vulnerability to both spontaneous errors and external suggestion, especially in the moments soon after use. While the buzz fades, some memory distortions may remain, complicating legal cases and personal realities.
This study isn’t anti-cannabis — it’s pro-truth. As legalization spreads, science must keep pace, ensuring that policies, courtrooms, and the public understand how cannabis affects not just the body, but the mind.
