A reversal occurred recently, with 57% of Americans supporting and 37% opposing cannabis legalization during 2016. Support for legalization appears to be transgenerational, with the largest shift observed in generations born during or after the 1940s (i.e., Baby Boomers, Generation X, Millennials), but also observed to a lesser extent among those born from mid-1920 to mid-1940 (i.e., the Silent Generation). Consistent with these trends, 28 U.S. states have passed medical marijuana laws and 8 have legalized recreational use for adults over the age of 21. Individuals who use both cannabis and tobacco exhibit higher brain levels of FAAH, the enzyme that degrades anandamide, compared to those using cannabis alone.
Acute effects
This results in reduced anandamide, a molecule involved in mood regulation, potentially contributing to increased anxiety, depression, and difficulty quitting cannabis among co-users. PET brain scans revealed that people who used both tobacco and cannabis had higher levels of FAAH, relative to people who only used cannabis. FAAH is the enzyme that breaks down anandamide, a naturally occurring molecule sometimes called the « bliss molecule » for its role in mood and stress regulation. More FAAH means less anandamide, a pattern previously linked to anxiety, depression and relapse when trying to quit cannabis.
Hearing Voices May Stem from the Brain Misreading Its Own Inner Speech
- Among illicit substances used by people with ADHD, cannabis is the most commonly used (203,204), providing opportunities for researchers to design cohort studies on the effects of cannabis in patients with ADHD.
- Although such studies have been valuable in advancing research in this area, they have an important limitation – they preclude making strong causal inferences between use of cannabis and declines in neuropsychological functioning.
- Independent samples t tests and Χ2 analyses were performed to assess potential univariate differences in the sociodemographic characteristics between the cannabis users and controls.
- Additionally, epilepsy is common in ASD (20–30%) and more prevalent in individuals with autism-like behavior resulting from particular genetic predispositions, such as Angelman syndrome, Rett syndrome, or Dup15q syndrome (208).
“As cannabis use continues to grow globally, studying its effects on human health has become increasingly important. While tobacco-smoking rates are declining overall, most people who use cannabis also use tobacco, the researchers note. Most studies have looked at cannabis and tobacco in isolation, Rabin added, leaving a gap that this preliminary study begins to address. People who use both cannabis and tobacco show distinct brain changes compared to those who use cannabis alone, according to a new study led by McGill University researchers at the Douglas Research Centre.
Studies without Neuropsychological Data Prior to Cannabis Use Initiation
In Canada, about one in 20 people who used cannabis in the past year are considered at risk for cannabis use disorder. “What surprised us was how strong the effect was, and how different it was from those who only used cannabis, compared to those who used both tobacco and cannabis,” said co-author Romina Mizrahi, Professor of Psychiatry and director of the McGill Research Centre for Cannabis. In Canada, about one in 20 people Cannabis and Brain who used cannabis in the past year are considered at risk for cannabis use disorder. « Identifying this mechanism is an important step toward finding targets for future medications to treat cannabis use disorder, especially among those that co-use tobacco. Right now, the only available treatments are behavioral therapies such as counseling, » she said. The University of Colorado Anschutz Medical Campus is a world-class medical destination at the forefront of transformative science, medicine, education and patient care. Evidence demonstrates that low levels of anandamide, a prominent endocannabinoid, correlate with worse clinical outcomes.
Finally, functional connectivity of the ventral striatum and midbrain, key brain areas for reward circuitry, as well as the brainstem and lateral thalamus was stronger in cannabis users than in controls (38,71,96). T2-weighted flair identified white matter hyperintensities and periventricular white matter hyperintensities. Diffusion MRI derived measures of white matter volume and white matter microstructure (such as FA, MD, axial diffusivity (L1), radial diffusivities (L2, L3) and mode of anisotropy from DTI, and intracellular volume fraction, isotropic volume fraction, and orientation dispersion).
Does Cannabis Use Cause Declines in Neuropsychological Functioning?: A Review of Longitudinal Studies
- From a more biological perspective, use of cannabis during critical developmental periods may cause persistent, long-term alterations in brain structure and brain function.
- In a preclinical study that tested the efficacy of CBD in a mouse model for Dravet syndrome, CBD reduced both seizures and ASD behaviors (209).
- There is substantial evidence that acute administration of cannabis or THC adversely affects executive function.
- To test for the presence of horizontal pleiotropy, a violation of a key MR assumption, we used the MR-Egger intercept test.
- Cannabis (Cannabis sativa) has been used for centuries as a source of fibers, food, oil, and medicine, as well as for recreational and religious purposes (1).
- Other subcortical assessments found that cannabis users had similar (60,62) or larger cerebellar volumes (44,58) than nonusers.
Additionally, the raw MRI data that had the wrong dimensions, were corrupted, missing, or otherwise unusable were not processed any further. Neuroscience News is an online science magazine offering free to read research articles about neuroscience, neurology, psychology, artificial intelligence, neurotechnology, robotics, deep learning, neurosurgery, mental health and more.
Early, heavy use may then interfere with educational and vocational training, leading to long-term consequences in adulthood. From a more biological perspective, use of cannabis during critical developmental periods may cause persistent, long-term alterations in brain structure and brain function. Some studies suggest that the effects of cannabis use during adolescence could be more serious than during adulthood (57) because it may alter the trajectory of brain development (24). AURORA, Colo. (Jan. 28, 2025) – A new study published today in JAMA Network Open explores the effects of both recent and lifetime cannabis use on brain function during cognitive tasks. Self-report questionnaires and laboratory risk-taking tasks have demonstrated differences between cannabis users and non-users, possibly related to the severity of cannabis use.
Across studies, IQ and episodic memory performance were the measures most likely affected, although results varied depending on the study. Regardless of the neuropsychological ability assessed, it is important to consider the magnitude of effects observed across studies, which ranged from about 1/5 to 1/2 of a SD unit. Nonetheless, adverse consequences of cannabis use, including on psychosocial and academic outcomes, are well documented (Lynskey & Hall, 2000; National Academies of Sciences & Medicine, 2017; Volkow et al., 2014).
CB1 are located throughout the cortex and densely concentrated in numerous brain regions important for cognition and psychomotor functioning (Glass, Dragunow, & Faull, 1997). Not surprisingly, the effects of cannabis on neuropsychological functioning have been a topic of considerable interest for many decades. Despite numerous studies, the onset, magnitude, and duration of the effects of cannabis on neuropsychological function, and the conditions under which adverse effects are exacerbated, continue to be debated. Understanding its adverse effects on neuropsychological functioning continues to be critically important.
“Identifying this mechanism is an important step toward finding targets for future medications to treat cannabis use disorder, especially among those that co-use tobacco. Unlike THC, which is psychoactive and is self-administered by rats (e.g. (26),), CBD is considered non-psychotropic and inhibits drug-seeking and self-administration in animal models (26,27). CBD does not bind to the orthosteric binding sites of CB1 and CB2 receptors with high affinity (27–29), but acts as an allosteric inhibitor of both cannabinoid receptors subtypes (27,30,31).
Statistical analyses
These regions of the brain are involved in important cognitive functions such as decision-making, memory, attention and emotional processing. Increased risk for substance use, abuse or dependence of many illicit substances has been well-documented in adolescents and adults with a childhood diagnosis of ADHD, further clouding investigations of the effects of cannabis per se on the brain in this patient population (201–203). Among illicit substances used by people with ADHD, cannabis is the most commonly used (203,204), providing opportunities for researchers to design cohort studies on the effects of cannabis in patients with ADHD. Although it is crucial to understand how cannabis use interacts with the neurocognitive vulnerabilities related to ADHD, ethical considerations would preclude assigning pediatric patients with ADHD to receive cannabis in the absence of previous use.
Yet some formulations of cannabinoid compounds are FDA-approved for medical uses, including applications in children. People who use both cannabis and tobacco show distinct brain changes compared to those who use cannabis alone, according to a new study led by McGill University researchers at the Douglas Research Center. However, Gowin mentions their research also suggests that abstaining from using cannabis before doing a cognitive task could help to improve performance. “People need to be aware of their relationship with cannabis since abstaining cold turkey could disrupt their cognition as well.
