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How Cannabis Impacts Health & the Potential Risks | Dr. Matthew Hill

Andrew HubermanAndrew Huberman
Science & Technology8 min read233 min video
Jul 8, 2024|814,305 views|12,778|2,167
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TL;DR

Dr. Matthew Hill discusses cannabis's neurobiology, effects, risks, and benefits, clarifying THC, CBD, and psychosis.

Key Insights

1

THC (Delta-9-tetrahydrocannabinol) is the primary psychoactive compound in cannabis, acting on widespread CB1 receptors in the brain to produce intoxicating effects, including euphoria, altered perception, and increased appetite.

2

CBD (cannabidiol) is non-intoxicating and does not directly bind to CB1 receptors. It has demonstrated efficacy in treating specific pediatric epilepsies (e.g., Dravet syndrome) possibly by blocking adenosine reuptake, but its precise mechanism of action is still being researched.

3

Endocannabinoids like anandamide and 2-AG are naturally produced by the body and play a crucial role in maintaining homeostasis, dynamically regulating neurotransmission. THC broadly activates CB1 receptors, leading to widespread effects, unlike the localized action of endocannabinoids.

4

Cannabis consumption methods significantly impact onset and duration: inhaled cannabis acts quickly (2-5 minutes) with a shorter high (2-4 hours), while edibles have a delayed onset (30-90 minutes) and prolonged effects (4-8 hours) due to liver metabolism producing more potent metabolites.

5

While anecdotes suggest different "strains" (Indica vs. Sativa) have distinct effects, scientific evidence, including chemical analyses, indicates these are botanical terms and don't correlate with specific chemical profiles or subjective outcomes. Expectancy bias likely plays a significant role in perceived differences.

6

Cannabis use disorder can develop, with higher rates among frequent users. The risk of psychosis and schizophrenia is a complex debate: cannabis doesn't cause schizophrenia de novo but can trigger or accelerate its onset in individuals with a genetic predisposition, especially with high-potency products and early initiation.

THE BIOLOGICAL FOUNDATIONS OF CANNABIS

Dr. Matthew Hill, an expert in cannabis biology, explains that cannabis is a plant with a rich history of medicinal and recreational use. Its primary psychoactive component is Delta-9-tetrahydrocannabinol (THC), which dictates the intoxicating effects. Other cannabinoids like Cannabidiol (CBD) are non-intoxicating, and numerous other minor cannabinoids and terpenes contribute to the plant's complex chemistry, potentially influencing its effects, a concept often referred to as the 'Entourage Effect.' However, the specific biological roles of most of these compounds are still poorly understood.

THC AND THE ENDOCANNABINOID SYSTEM

THC primarily exerts its effects by acting on Cannabinoid type 1 (CB1) receptors, which are widely distributed throughout the brain. This system exists naturally in the body, utilizing endogenous cannabinoids (endocannabinoids) like anandamide and 2-AG, often likened to a homeostatic 'thermostat' that regulates neuronal activity. Unlike conventional neurotransmitters, endocannabinoids operate in a retrograde fashion, being released by the postsynaptic neuron to modulate neurotransmitter release from the presynaptic neuron. THC's impact, particularly that of high-potency cannabis, is a widespread, indiscriminate activation of these receptors, disrupting the finely tuned, spatially and temporally specific actions of endogenous cannabinoids, leading to altered information processing and perception.

THE NATURE OF THE 'HIGH' AND TIME PERCEPTION

The 'high' experienced from cannabis is complex, often involving euphoria, positive mood, altered environmental perception, and introspection. However, it can also induce dissociative states. The intensity correlates with THC concentration, measured using visual analog scales in laboratory settings. Cannabis is known to disrupt time perception, causing individuals to perceive longer durations than have actually passed. While the exact neural mechanisms for this temporal distortion are not fully understood, animal studies involving timed behavioral tasks corroborate this effect, showing altered responses to temporal cues under cannabinoid influence.

CANNABIS AND APPETITE: THE MUNCHIES EXPLAINED

Cannabis's appetite-stimulating effects, commonly known as 'the munchies,' are mediated through CB1 receptors located in hypothalamic feeding circuits, such as those involving agRP neurons. THC can disinhibit these neurons, promoting food-seeking behavior. Furthermore, cannabis engages reward circuitry, making palatable foods more appealing, and can even override satiety signals. Research indicates that THC can 'trick' the brain into a fasted state, maintaining the high reward value of food despite actual satiety. This effect often drives the consumption of high-calorie, high-fat, and high-carb foods.

MEMORY, FOCUS, AND STATE-DEPENDENT LEARNING

Acutely, particularly during intoxication, cannabis can impair short-term memory, affecting recall and consolidation processes. However, there's less compelling evidence for long-term, permanent cognitive deficits in regular users when sober. The impact on memory can be less robust in chronic users, possibly due to state-dependent learning or tolerance. While some users report enhanced focus with cannabis, scientific evidence explicitly studying this is scarce, and anecdotal claims may be influenced by expectancy bias rather than direct pharmacological effects on attention.

ROUTES OF ADMINISTRATION AND DOSING CONSIDERATIONS

The route of cannabis administration significantly alters its onset and duration. Inhalation leads to rapid onset (2-5 minutes) and a shorter high (2-4 hours), as THC quickly enters the bloodstream and crosses the blood-brain barrier. Oral consumption via edibles results in a delayed onset (30-90 minutes) and prolonged effects (4-8 hours), due to first-pass metabolism in the liver producing 11-hydroxy-THC, a more potent metabolite. Many adverse events from cannabis, particularly overconsumption and unintentional pediatric ingestions, are linked to edibles because users often redose before the initial effects fully manifest, leading to over-intoxication due to the delayed onset.

CANNABIS POTENCY, TOLERANCE, AND DRUG TESTING

Cannabis potency has significantly increased, from ~5% THC in the 1970s to 20-30% currently. Despite this, studies show that many users self-titrate their intake when inhaling, often maintaining similar blood THC levels (~100 ng/mL) regardless of potency by adjusting the number of 'tokes.' However, concentrates (up to 90%+ THC) are challenging to titrate, leading to much higher blood levels (200-300 ng/mL) and a greater propensity for adverse effects and faster development of tolerance. Cannabis metabolites are lipophilic and can store in fat tissue, making them detectable in drug tests for extended periods (e.g., 30 days or more), with physical activity potentially releasing stored THC and causing a positive test result.

HORMONAL IMPACTS AND REPRODUCTIVE HEALTH CONCERNS

The effects of cannabis on hormones, such as testosterone, estrogen, and prolactin, are complex and inconsistent across studies. While some research suggests transient drops in testosterone after cannabis use, levels typically remain within the normative range. Claims of cannabis-induced gynecomastia (male breast tissue growth) are largely anecdotal and not well-supported by scientific literature. Regarding reproductive health, in vitro and animal studies indicate potential negative impacts on sperm quality (motility, capacity), though human data is mixed. For individuals struggling with conception, discontinuing cannabis use is a reasonable recommendation.

CANNABIS USE DURING PREGNANCY

Estimates suggest a significant percentage of pregnant women (potentially around 10%) use cannabis, sometimes unknowingly in early pregnancy. While most stop upon realizing they are pregnant, some continue, often for anti-nausea effects, preferring cannabis over pharmaceuticals due to historical tragedies like thalidomide. This is concerning, as dispensaries have been known to irresponsibly recommend cannabis for morning sickness. Unintentional pediatric consumption of cannabis edibles, particularly gummies, has led to increased emergency room visits following legalization, carrying serious legal ramifications for parents in some regions, highlighting the need for proper storage and public education.

CANNABIS AND PSYCHOSIS: UNPACKING THE CAUSALITY DEBATE

Cannabis can acutely induce psychotic-like episodes, though these are relatively rare compared to anxiety attacks, which are more common with overconsumption. The dose-dependent effects are biphasic: low doses may reduce anxiety by quieting excitatory transmission, while high doses can saturate inhibitory neurons, leading to pro-anxiety or panic responses. The link between cannabis and chronic psychotic disorders like schizophrenia is complex and contentious. While individuals with schizophrenia use cannabis at higher rates, and cannabis can trigger an earlier onset or worsen the prognosis in genetically predisposed individuals, evidence does not strongly support cannabis as a direct cause of schizophrenia. Factors like genetic predisposition, self-medication, and other stressors likely play significant roles.

THE INDICA VS. SATIVA DILEMMA AND THE EXPECTANCY BIAS

The terms 'Indica' and 'Sativa' are botanical classifications related to plant morphology, not chemical composition or subjective effects. Extensive chemical analyses show greater variability within these categories than between them, suggesting no unique chemical profile defines an Indica or Sativa strain. Dr. Hill posits that perceived differences in effects (e.g., Sativa being energizing, Indica relaxing) are largely attributable to expectancy bias. Users' beliefs, often influenced by dispensary information or anecdotal reports, profoundly shape their subjective experience. Blinded clinical trials are needed to definitively ascertain if different cannabis compositions produce distinct, reproducible subjective effects.

CBD'S MECHANISM AND THERAPEUTIC APPLICATIONS

CBD does not directly bind to CB1 or CB2 receptors, and its mechanism of action is still not fully understood. It is, however, highly effective in treating specific forms of pediatric epilepsy, such as Dravet syndrome, at high doses, leading to significant seizure reduction. This therapeutic efficacy has contributed to its reclassification and widespread availability. One proposed mechanism involves CBD's ability to block adenosine reuptake, leading to increased adenosine levels, which can have sedative and anti-inflammatory effects. Unlike THC, CBD was largely bred out of cannabis strains until recent medical interest spurred its specific cultivation, with most available cannabis being THC-dominant.

THE REGULATORY CHALLENGES AND PUBLIC HEALTH IMPLICATIONS

The evolving legal status of cannabis presents significant regulatory challenges. Discrepancies in federal versus state regulations, especially in the US, lead to a lack of standardization in product quality and safety, as seen with issues like vitamin E acetate in vape products. Standardized dosing units, similar to alcohol, are crucial for public safety, particularly with edibles. There's a notable gap in public education, with many users relying on budtenders for information, who often lack formal training. Dr. Hill advocates for mandatory educational courses for cannabis retailers to ensure informed consumer choices and promote harm reduction, distinguishing between legal status and inherent product safety.

Common Questions

Cannabis is a plant containing many cannabinoids, terpenes, and other molecules. The primary psychoactive compound is Delta-9 Tetrahydrocannabinol (THC), which dictates the intoxicating effects. Cannabidiol (CBD) is another non-intoxicating cannabinoid with potential therapeutic effects, and terpenes contribute to the plant's smell and flavor, potentially influencing its overall effects.

Topics

Mentioned in this video

People
Andrew Huberman

Host of the Huberman Lab podcast and a professor of Neurobiology and Ophthalmology at Stanford School of Medicine.

Matthew Hill

Guest on the podcast and a professor of Cell Biology and Anatomy at the University of Calgary, whose lab studies cannabis effects.

Marcus Heilig

Colleague of Dr. Leah Mayo, involved in trials with FAAH inhibitors during her post-doctoral work in Sweden.

Donald Tashkin

A researcher in California, potentially at UCLA, who conducted long-term studies on cannabis smokers and found no clear association with lung cancer.

Angela Bryan

A researcher in Colorado who, along with Kent Hutchinson and Cinnamon Bidwell, developed the 'Cannavan' for real-world cannabis research.

Ryan McLaughlin

A researcher at Washington State University who pioneered vape chambers in rats to study cannabis self-administration.

Zach Knight

From HHMI and UCSF, previously a guest on the Huberman Lab podcast, who discussed neurons in the hypothalamus.

S. Patel

Now at Northwestern, previously at Vanderbilt, who conducted studies on rodents demonstrating that reductions in endocannabinoid function produce anxiety, reversible by THC.

Raphael Mechoulam

Scientist who isolated and discovered THC in 1964 and later isolated anandamide, considered the 'grandfather of the cannabinoid field'.

Gavriel Marano

European researcher who created genetic lines of mice with CB1 receptor deletions from specific neuron types.

Beat Lutz

European researcher who created genetic lines of mice and conducted studies to understand how CB1 receptors influence anxiety by their location on excitatory or inhibitory neurons.

Leah Mayo

A colleague of Dr. Hill in Calgary who worked with Marcus Heilig in Sweden on FAAH inhibitor trials, and later on PTSD trials.

Kent Hutchinson

A researcher in Colorado who, along with Angela Bryan and Cinnamon Bidwell, pioneered the mobile 'Cannavan' to study cannabis use in ecological settings.

Cinnamon Bidwell

A researcher in Colorado who, along with Kent Hutchinson and Angela Bryan, introduced the 'Cannavan' to study cannabis use in natural environments.

Moreen Dow

A New York Times reporter who famously had an adverse experience with a high-dose cannabis edible in Colorado, highlighting unpredictable dosing.

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