A number of high-quality longitudinal studies have demonstrated that cannabis use negatively affects several cognitive domains. These effects persist for up to days or weeks following abstinence.
Residual impairments on verbal learning and memory, response inhibition, and psychomotor speed are a common consequence of cannabis exposure. The impairments are typically small to moderate and occur in a dose-response fashion.
Memory
Cannabis has been shown to have a negative impact on various cognitive functions, including memory. This includes deficits in the ability to recall information, such as dates or numbers. However, these effects can be mitigated by the use of cannabidiol (CBD) – an ingredient found naturally in marijuana.
In order to better understand the impact of cannabis on cognition, it is important to review the evidence for short-term and long-term effects. The latter includes results from studies that examine the effect of daily or near-daily cannabis consumption on cognition.
While the effects of alcohol, cocaine and methamphetamine on cognitive function are relatively well established, the research into the effects of cannabis is far less extensive. As a result, the results of studies on residual effects are more difficult to interpret, but they generally indicate that cannabis causes relatively small deficits in several cognitive domains.
The most consistent impairments appear to be in aspects of memory, such as memory for names and locations or in tasks assessing reaction time. Some studies also found that cannabis use impaired performance on a number of different executive functions, such as attention and response inhibition.
One study compared the effect of D9-THC and D9-THC with CBD on several cognitive tests, finding that D9-THC induced significantly more impairments in working memory than placebo (44). Another study found that D9-THC with CBD induced significantly more impairing effects on episodic memory than D9-THC alone, but did not show any difference in performance on a variety of other working memory measures.
Some studies have found that heavy cannabis users are more likely to develop a psychotic condition such as schizophrenia. This has been interpreted as a direct result of the psychiatric effects of cannabis, although there are also possible links to long-term psychological problems.
There are many factors that influence the impact of cannabis on cognition. These include the frequency of use and whether or not patients are abstinent. In addition, the timing of testing may also have an effect. For example, some studies have examined patients after a very short treatment period or when they were acutely intoxicated. In these cases, the effects of cannabis on memory may have been limited to the time of intoxication.
Attention
Acute cannabis/D9-THC exposure results in small to moderate deficits (g = 0.69; g = 0.51; g = 0.51, respectively) in verbal learning and memory, as well as small impairments in working memory and processing speed. These effects are more pronounced in acute phase of cannabis intoxication, but they persist days following abstinence.
Several studies have shown that heavy cannabis users are more impaired in attention, concentration, decision-making, inhibition, and impulsivity than light cannabis users. These deficits may be influenced by the context in which they are experienced and the duration of exposure.
These deficits are similar to the residual effects of alcohol, cocaine and methamphetamine in the short-term. However, research on the long-term cognitive effects of cannabis is less extensive.
The most recent evidence suggests that the earliest onset of cannabis use is associated with cognitive impairments, particularly with respect to memory and executive functions. These impairments may be premorbid, i.e., existing before a person becomes a regular user.
Acute cannabis/D9-THC also impairs the ability to learn new information, especially when learning is based on encoding and consolidation (e.g., recitation and retrieval), and it can promote impulsivity. In addition, these impairments can negatively impact decision making and risk-taking.
Some studies have shown that the amplitude of cognitive impairments is dose-dependent, with moderate deficits observed in daily cannabis users, and mild deficits in light and occasional users. These findings are similar to those found with alcoholic or opioid-induced impairments in IQ tests and in non-verbal cognitive tasks.
Although some of these effects are not considered detrimental, the potential for cannabis to have long-term cognitive negative effects is an important concern. This is due to the fact that heavy cannabis use can lead to deterioration in learning and memory, as well as other cognitive domains such as attention, executive function and processing speed.
Moreover, cannabis can be more harmful to learning and memory when used in combination with other substances such as alcohol or nicotine. These substances interact with the brain’s endogenous cannabinoid system and alter the functioning of the parahippocampal gyrus, thalamus and midbrain regions.
Decision Making
Cannabis is a widely used drug with numerous psychological and cognitive effects. Although it has been used for thousands of years, a growing body of evidence suggests that its use can have significant adverse effects on mental health and cognition.
Acute impairments of attentional and working memory function have been well-documented. Recovery of these functions in the acute stage is likely after a month or more of abstinence, but long-term cannabis users exhibit persistent deficits in attentional processing.
In this study, we examined the effect of chronic cannabis use on decision making and impulsivity in current cannabis users without comorbid psychiatric disorders. This group of 35 cannabis users and 35 non-users were compared using behavioral measures of decision-making (Iowa Gambling Task), reward discounting (Delay Discounting Task), choice-outcome learning (the Probabilistic Reversal Learning Task) and a questionnaire assessment of trait impulsivity (Barratt Impulsiveness Scale).
The results indicated that both cannabis users and non-users were less successful at making decisions on the Iowa Gambling task and the Delay Discounting task. In addition, the cannabis users endorsed higher impulsivity scores on the Barratt Impulsiveness Scale than non-users.
It has been argued that these findings are consistent with the effects of cannabis on executive functions, but the mechanisms responsible for these cognitive impairments remain unclear. These findings also suggest that more studies are needed to assess the long-term impact of cannabis on cognitive functioning.
We searched four databases for relevant literature on the impact of cannabis-based medicines on cognitive functioning measured by recognised cognitive tests in human adults. The searches were based on the keywords “cannabis”, “cognitive” and “effects”.
There were 247 published papers in the database covering 43 different cognitive tests, which included several types of attentional and memory functions. The tests were diverse and ranged from the Symbol Digit Modalities Test, the Trial Making Test (TMT-A, B) to the PASAT.
The majority of the studies were randomized, double-blind and placebo-controlled. Most had short treatment periods and delivered cannabis either by smoking or vaping. All of them had relatively high doses, with most containing more than 30 mg THC/day.
Learning
THC, the primary psychoactive compound in cannabis, acts on brain receptors called endocannabinoid systems. These receptors are found in the prefrontal and limbic regions of the brain and they are responsible for many important functions such as reward, motivation, learning and memory.
However, there is also evidence that it has a negative impact on certain higher level cognitive functions (also known as executive function). These include: – planning and problem solving – attention and concentration – decision making – memory and information processing – social cognition – emotions and behavior management
In recent years, the research on the effects of cannabis on cognition has accelerated. It is now clear that short-term impairments of basal cognitive domains, such as learning and memory, attentional control, motor inhibition, and verbal fluency occur following acute cannabis intoxication.
These deficits persist for a period of time and can be corrected with sustained abstinence from cannabis. In addition, chronic, heavy cannabis use can impair impulsivity and working memory, but these deficits disappear with prolonged abstinence.
The effects of cannabis on learning and memory may be influenced by a number of factors including: – changes in the brain’s structure due to THC intoxication – a lack of motivation that can lead to increased laziness or decreased drive – problems with concentration and focus.
As a result, it is difficult to tell how well people learn while high and how that will affect their performance in school and work. If you are experiencing issues with your learning when you are under the influence of cannabis, it is important to seek treatment.
Cognitive remediation therapy can help people who are experiencing negative effects on their memory, concentration and decision-making while under the influence of cannabis. It involves exposing patients to cognitive training-based strategies that can improve their underlying neuropsychological functions affected by marijuana use, such as attention span, memory, information processing, executive function and decision-making skills.
There is still a need to conduct more studies on the impact of long-term or chronic use of oral cannabis-based medical preparations on cognitive functioning, particularly with respect to multiple sclerosis. These studies require a broader range of measures and sample composition than are currently available.
