Our memories are fickle beasts. Sometimes, we just cannot remember an instance from childhood, a song, a name, etc. These days, however, you needn’t wonder about most things since, no doubt, your smartphone is at arm’s length.
Remembering something that never happened, however, portends a frightening array of doubt, disbelief, adamancy, and confusion. While some false memories might be benign or silly, others might drive you to your literal wit’s end. Memory is an illusion. And, your memory can be hacked. 
Cannabis, or rather, delta-9-tetrahydrocannabinol (THC) has been implicated as causing memory impairment, but stances like that are never really cut and dry. For example, one study reported that episodic memory (recalling and mentally reliving episodes from your past) was impaired by THC, while working, or short-term memory was generally unaffected.  A different study found that dosing with THC or THC and CBD (cannabidiol) affected both memory types.  And further confounding the spectrum of possibilities, when low doses of THC were given to mature (12 months) and elderly (18 months) mice, their age-induced cognitive decline was reversed.  The little murine, mental Benjamin Buttons…
Toss in memory-restoration attributes of terpenes like the pinene isomers  and β-caryophyllene , and the full story seems about as perplexing as a cut-up novel by William S. Burroughs. THC is said to impair memory in the young, might restore memory in the old, might cause you to forget that you were even reading this, or to eject some newfound connection to a resurrected memory from 13 years ago.
A 2020 study evaluated cannabis’s influence on the generation of memories that never happened.  The judicial intro discussed the need for reliable testimony during legal proceedings and the obvious havoc false memories can wreak in the courtroom. The authors referenced a study that evaluated the proportion of eyewitnesses who are intoxicated.  The data showed 18% of witnesses (or victims) were intoxicated via cannabis. Would these people identify with events that never happened?
Cannabinoid 1 receptors located in the hippocampus (brain region heavily involved in memory) could “underlie the formation of incidental associations, which would predict an increase in false memories.”  These fictitious “memories” can be spontaneous, coming straight out of our heads, or suggestion-based, coming from someone else’s head and mouth.
Spontaneous memories were mined by providing an orally communicated word list to participants who then needed to repeat the words back. Participants often add related words (lures) that they “remember” as part of the original list but were never actually uttered.
The researchers turned to virtual reality (VR) to introduce suggested memories. Traditional methods for assessing suggested memories can include mock crimes and staged events. VR, however, provided “high degrees of realism, ecological validity, and feelings of presence.”  Following the events, like a VR purse snatching, interviewers probed participants for accounts of presented and non-presented details as well as leading questions on things that didn’t happen, meant to escort the participant into the make-believe.
People actively under the influence of cannabis showed increased false memories. Spontaneous false memories continued even after a week when participants were “sober” again. The researchers hypothesized that THC impaired the intake of information, “thereby also reducing memory for similar, easily confusable items.” 
Suggested false memories also increased, both for the leading inquiries about suggested details and to neutral questions about events that never happened. Intoxicated participants were more likely to answer “yes” to all questions. These false memories, however, dissipated after a week had elapsed, “indicating that THC-induced impairments might be most detrimental to retrieval.”  Countering this, though, the researchers found that the placebo group worsened over time, and ultimately ended up revealing greater similarity to the cannabis group after one week.
Our ability to recall the minutiae many moons after the fact wanes as more time passes after an event. Our memories degrade and are concomitantly more affected by misinformation. This finding balanced the statistical scales and thus, no differences in memory were found.
Hippocampal CB1 receptors are thought to be significant in the cognitive effects induced by cannabis ingestion. The authors list the effects as “a loosening of associations, fragmentation of thought, and heightened distractibility.”  Or, the “impaired” person might think they came up with a specific thought when, in fact, it came from external sources. Thinking that a thought is your own when it came from outside of your head? I think I saw that on The X-Files…
- Shaw, J. and Porter, S. “Constructing Rich False Memories of Committing Crime.” Psychological Science, vol. 26, no. 3, 2015, pp. 291-301. [Journal Impact Factor = 4.902; Times Cited = 56 (SemanticScholar)]
- Curran HV, et al. “Cognitive and Subjective Dose-Response Effects of Acute Oral Δ9-Tetrahydrocannabinol (THC) in Infrequent Cannabis Users.” Psychopharmacology, vol.164, no.1, 2002, pp. 61-70. [Journal Impact Factor = 3.875; Times Cited = 188 (SemanticScholar)]
- Morgan, C. et al. “Individual and Combined Effects of Acute Delta-9-Tetrahydrocannabinol and Cannabidiol on Psychotomimetic Symptoms and Memory Function.” Translational Psychiatry, vol. 8, 2018, pp. 181-190. [Journal Impact Factor = 5.182; Timed Cited 14 (SemanticScholar)]
- Bilkei-Gorzo, A. et al. “A Chronic Low Dose of Δ9-Tetrahydrocannabinol (THC) Restores Cognitive Function in Old Mice.” Nature Medicine, vol. 23, 2017, pp. 782–787. [Journal Impact Factor = 30.641; Times Cited = 43 (SemanticScholar)]
- Lee, G. et al. “Amelioration of Scopolamine-Induced Learning and Memory Impairment by α-Pinene in C57BL/6 Mice.” Evidence-Based Complementary and Alternative Medicine, vol. 2017, no. 2017, ID 4926815, 9 pages. [Journal Impact Factor = 2.064; Times Cited = 15 (SemanticScholar)]
- Cheng, Y. et al. “β-Caryophyllene Ameliorates the Alzheimer-Like Phenotype in APP/PS1 Mice through CB2 Receptor Activation and the PPARγ Pathway.” Pharmacology, vol. 94, 2014, pp. 1-12. [Journal Impact Factor = 1.615; Times Cited = 38 (SemanticScholar)]
- Kloft, L. et al. “Cannabis Increases Susceptibility to False Memory.” PNAS, vol. 117, no. 9, pp. 4585–4589. [Journal Impact Factor = 9.58; Times Cited = 0 (SemanticScholar)]
- Evans, J. et al. “Intoxicated Witnesses and Suspects: Procedures and Prevalence According to Law Enforcement.” Psychol. Public Policy Law, vol. 15, 2009, pp. 194–221. [Journal Impact Factor = 2.219; Times Cited = 39 (SemanticScholar)]
Image Credit: Vox