Research pertaining to consistent marijuana use and its effect on memory is ongoing, but the fact that it has an impact on short-term memory is pretty obvious, per Harvard Health. It all has to do with how the different compounds in marijuana affect your brain. While cannabidiol (CBD) can be beneficial for those with anxiety, THC can attach to certain receptors in your brain responsible for memory formation and temporarily disrupt neural signaling. This is why someone who’s high on weed might display a lack of interest in things, or have difficulty concentrating or grasping something they learned (via The Conversation).
As for the effects of marijuana use on long-term memory, research led by Matthew Smith (which was also published in the journal Hippocampus) is relevant. Even though the young adults in the study had abstained from cannabis use for about two years, when they were tested for long-term memory using assessments, they performed poorly when compared with participants who’d never used cannabis (via TIME).
Interestingly, a 2019 study published in the journal PNAS found a link between just one puff of weed and “false memories”: remembering something that wasn’t there or remembering something differently than how it happened, per CNN. “We are all prone to the formation of false memories, independent of cannabis use. The susceptibility for false memory, however, increases with cannabis. Under cannabis, users can easily accept fake truths for true memory,” explained Johannes Ramaekers, lead author and professor of psychopharmacology at Maastricht University in the Netherlands.