Cannabidiol, also known as CBD, is one of the many active ingredients present in the cannabis plant. Cannabidiol (Epidiolex®) is approved in the US for the treatment of two rare forms of childhood epilepsy. Preclinical studies have suggested potential neuroprotective properties of cannabidiol, including improved cognitive functions and decreased inflammation. However, most clinical studies in humans have shown a lack of cognitive improvement, and no data exist for long-term treatment. Cannabidiol can affect the activity of many medications, and side effects are common, including liver problems and gastrointestinal issues.
Many clinical trials have been carried out, but most studies have been small and short in duration, with mixed or inconclusive results on cognitive outcomes. No data exist for long-term treatment in healthy adults. Our search identified:
No studies have tested whether cannabidiol can prevent dementia or cognitive decline. A meta-analysis of 16 randomized controlled clinical trials (in adults with social anxiety, psychosis, nicotine dependence, pre-schizophrenia, chronic pain, or in healthy adults) reported that a single dose of cannabidiol resulted in a small but significant impairment in cognitive performance compared to placebo [1]. However, cannabidiol treatment did not affect objective measures of cognitive performance, including memory, driving performance, information processing, attention, or higher order cognitive functioning). Individual randomized controlled trials in healthy adults have shown inconsistent effects of cannabidiol on cognitive function. In one double-blind randomized controlled trial of 27 healthy adults, cannabidiol treatment for 2 days did not have any significant effects on cognitive measures or mood [2]. In a different randomized controlled trial of 34 healthy young adults, a single vaping dose of cannabidiol improved episodic memory but had no effect on measures of attention or working memory [3]. In a different randomized controlled trial of 17 healthy adults, a single dose of cannabidiol did not impair simulated driving performance at most doses and assessments, but results were less conclusive with other doses and assessments [4]. Because most studies of cannabidiol assessing cognitive outcomes were small and short in duration, larger longer clinical trials are needed to evaluate the effects of cannabidiol on cognitive health.
Preclinical studies have shown that cannabidiol treatment prevents cognitive dysfunction in models of Alzheimer’s disease [5; 6; 7; 8], Parkinson’s disease [9], memory impairment [10], and brain injury [11]. Some proposed mechanisms include increased numbers of brain cells [11], increased levels of a protein (i.e., BDNF) that protects brain cells [11], decreased inflammation in the brain [8; 12], and decreased levels of proteins that drive cell death [13]. However, these proposed mechanisms have not been validated in humans.
Recreational use of cannabis seldomly causes permanent psychological disorders depending on the individual’s sensitivity, including cognitive impairment, anxiety, paranoia, and increased risks of psychosis or drug addiction [14]. Tetrahydrocannabinol (THC) appears to be responsible for many of these negative effects, while cannabidiol appears to counteract them [15].
The effects of cannabidiol in dementia patients remain unclear [16]. In a small randomized controlled trial of 15 Alzheimer’s patients with behavioral and psychological symptoms, cannabidiol treatment for 6 weeks improved neuropsychiatric symptoms, including hallucinations, anxiety, agitation, apathy/indifference, and irritability compared to placebo [17]. This study had a smaller than planned number of participants due to the challenges posed by the COVID-19 pandemic, and therefore, it was not statistically powered to assess effects on cognitive function. In another randomized controlled trial of 52 patients with a major neurocognitive disorder and associated behavioral disturbances, cannabidiol treatment (which also included THC) significantly reduced agitation and aggression [18]. However, some trends for higher rates of cognitive side effects were observed with the treatment, including memory issues, hallucinations, sleepiness, and confusion/disorientation.
Cannabidiol may negatively affect liver function [19; 20], and therefore, your doctor may monitor your liver enzyme levels before and during treatment [21]. Other common side effects include drowsiness, somnolence, sedation, decreased appetite, and gastrointestinal issues such as diarrhea [19; 22]. Cannabidiol interacts with many drugs, including anti-anxiety medications (e.g., citalopram, sertraline, alprazolam), anti-seizure medications (e.g., valproate), sleeping pills, opioid medications (e.g., buprenorphine, propoxyphene), lipid-lowering drugs (e.g., atorvastatin, lomitapide), blood thinners (e.g., clopidogrel), non-steroidal anti-inflammatory drugs (e.g., acetaminophen, diphenhydramine, naproxen), and drugs for multiple sclerosis (e.g., leflunomide, teriflunomide) [23].
NOTE: This is not a comprehensive safety evaluation or complete list of potentially harmful drug interactions. It is important to discuss safety issues with your physician before taking any new supplement or medication.
Cannabidiol (sold as Epidiolex®) is available by prescription to treat two rare forms of childhood epilepsy. In seizure disorders, the initial dose is 2.5 mg/kg twice daily taken orally, then increased to 5 mg/kg twice daily [23]. There are other cannabidiol-containing products on the market that are labeled as “dietary supplements”, but the amount of cannabidiol contained is not always reported accurately on the product label and they may contain cannabis constituents other than cannabidiol [24; 25].
Full scientific report (PDF) on Cognitive Vitality Reports
Check for drug-drug and drug-supplement interactions on Drugs.com.