In a previous article we discussed the use of cannabinoids in neurodegenerative disorders, and we’ll continue this series with today’s article, which investigates the effects of cannabidiol (CBD) and THC on memory.
Does cannabis affect memory?
We’ll start with this study published in 2010 in The British Journal of Psychiatry, which compares the effects of CBD and THC from smoked cannabis on acute memory. The existing literature indicates that cannabidiol and tetrahydrocannabinol, the two main components of the cannabis plant, have opposing effects on the human brain, THC being psychoactive, while CBD counteracts this effect and prevents one from getting high.
Tests on humans smoking to see if with THC and CBD
In this study, 134 cannabis users were tested before and after smoking cannabis. The THC content of the plants used by participants was similar in all users, so the participants were divided into two groups based on the level of cannabidiol in the smoked plant. The study found that the group who smoked cannabis with high THC and low CBD levels showed signs of memory impairments, while those who used cannabis with high CBD levels showed no memory impairment.
The authors of this study noted that “people in our study who smoked higher cannabidiol strains of cannabis did not show any acute deficit. Indeed their performance when intoxicated was virtually indistinguishable from that when drug free.” So it appears that cannabis affects memory in different ways, depending on the relative levels of CBD and THC.
Only one previous study in humans has assessed effects of cannabidiol on THC-induced memory impairments and it reported no interaction although it administered very much lower doses of THC and cannabidiol than were self-administered by our participants. Our findings are, however, consistent with recent research demonstrating the reversal of THC-induced memory deficits in rats by the CB1 receptor antagonist”.
CBD may reverse the effects of THC on memory
It is believed that THC’s effects on memory come from its interaction with the CB1 receptor, which is present in memory-related brain areas and is involved in modulating memory. Despite the reduced number of studies on the effects of cannabinoids on memory in humans, and on the limitations of the existing literature, research seems to suggest that administration of THC impairs all stages of memory, while CBD efficiently blocks the unwanted effects of the psychoactive compound.
So we know that THC disrupts short-term memory and makes it difficult to form new memories while high. Also, we know that this psychoactive compound prevents the consolidation of short-term memories into long-term ones. And we assume, based on the available research, that CBD is able to reduce the memory impairments caused by THC.
Studies on animals show the difference between THC and CBD effects
In an animal study published in the journal of Neuropharmacology, UK researchers showed that cannabis extracts rich in THC impair spatial working and short-term memory formation in rats, while CBD-rich extracts have no effect. Authors of this paper concluded that spatial working/short-term memory is not sensitive to CBD-rich extracts and that the memory deficits induced by THC-rich compounds are dependent on the CBD/THC ratio.
To conclude, most of the existing studies suggest that THC leads to memory impairments, but it appears that CBD has the potential to counter these effects.