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

Added: Jul 9, 2024

THC acts primarily on cannabinoid type 1 (CB1) receptors in the brain. These receptors are part of the endocannabinoid system, which helps maintain homeostasis. Endogenous cannabinoids like anandamide and 2-AG are produced naturally in the body and act on CB1 receptors. Unlike typical neurotransmitters that are released from one neuron to act on another, endocannabinoids are produced "on-demand" and act in a retrograde fashion, traveling backwards across synapses to regulate neurotransmitter release.

The psychoactive effects of cannabis can include euphoria, altered perception of time, increased appetite, and changes in sensory processing. The intensity depends on the THC content and individual factors. Cannabis with higher THC levels doesn't necessarily lead to stronger effects, as users tend to self-titrate their intake. However, cannabis concentrates with very high THC levels can overwhelm this self-regulation.

Routes of Administration and Effects

Inhaled cannabis, whether smoked or vaporized, produces effects within minutes that peak around 15-30 minutes and largely subside within 2-3 hours. Oral consumption via edibles has a much slower onset of 30-90 minutes, with effects potentially lasting 4-8 hours. Edibles produce lower blood THC levels but can lead to more intense and longer-lasting effects due to metabolism of THC to 11-hydroxy-THC in the liver. The delayed onset of edibles can lead to overconsumption if users don't wait long enough to feel effects before taking more.

Dr. Hill emphasizes that vaporizing cannabis flower may reduce some harms associated with smoking by avoiding combustion byproducts. However, vape pens using cannabis oil extracts have unknown long-term effects and have been associated with some cases of lung injury.

Medical Uses and Potential Benefits

While more research is needed, there is some evidence for medical benefits of cannabis, particularly for chronic pain, nausea, and certain forms of epilepsy. For pain, cannabis may not strongly reduce pain intensity but can make pain more tolerable by reducing its emotional impact. It may also help with sleep, which can improve overall quality of life for chronic pain patients.

For epilepsy, high doses of CBD have shown efficacy for certain pediatric seizure disorders in clinical trials. This led to FDA approval of a prescription CBD medication. However, the doses used medically are much higher than typical over-the-counter CBD products.

There is mixed evidence for cannabis in treating anxiety. While many users report it helps reduce anxiety and stress, high doses can potentially increase anxiety in some individuals. Dr. Hill's research suggests endocannabinoid deficiency could contribute to anxiety, and cannabis may help some users by "filling in" this deficiency. However, more research is needed to confirm this hypothesis.

For PTSD, some evidence suggests THC may help reduce nightmares and improve sleep quality, which could benefit overall symptoms. However, large-scale clinical trials are still lacking.

Potential Risks and Harms

Dr. Hill discusses several potential risks associated with cannabis use. While the link between cannabis and psychosis or schizophrenia is complex, he advises that individuals with schizophrenia or bipolar disorder, or those with a family history of these conditions, should avoid cannabis use. The evidence does not clearly show that cannabis directly causes schizophrenia in otherwise healthy individuals, but it may trigger earlier onset or worsen outcomes in those predisposed to the condition.

Smoking cannabis can cause lung damage, though the link to lung cancer appears weaker than with tobacco smoking. There may be cardiovascular risks, particularly for those with pre-existing heart conditions, as cannabis can cause changes in heart rate and blood pressure. A rare condition called cannabinoid hyperemesis syndrome can occur in some chronic users, causing severe cyclic vomiting.

Cognitive effects during acute intoxication are well-established, particularly on short-term memory and attention. However, long-term cognitive effects in regular users are less clear, with some studies showing minimal impairment when not acutely intoxicated.

Cannabis use disorder affects a minority of users but is a real concern. Weekly users may have around a 30% chance of developing problematic use patterns. However, cannabis addiction is generally considered less severe than addiction to drugs like opioids or cocaine.

Driving while under the influence of cannabis is dangerous and illegal. Effects on driving can last several hours after use, even when subjective intoxication has decreased.

CBD and the "Entourage Effect"

Dr. Hill expresses skepticism about many of the purported benefits of CBD, particularly at the low doses found in most commercial products. While high doses of CBD have shown efficacy for certain forms of epilepsy, there is limited evidence for its effects on anxiety, sleep, or pain at typical supplement doses. He suggests many of the reported benefits may be due to placebo effects.

The "entourage effect" theory suggests that the various compounds in cannabis work synergistically to produce effects beyond THC alone. While plausible, Dr. Hill notes there is limited clinical evidence to support this idea currently. The subjective differences users report between cannabis strains may be largely due to expectancy effects rather than meaningful chemical differences.

Legalization and Public Health

Dr. Hill discusses how cannabis legalization in Canada has impacted use patterns and public health outcomes. Overall use rates have increased somewhat, particularly among older adults, but teen use has remained relatively stable. Emergency room visits related to cannabis, particularly from edible overconsumption, have increased. However, arrest rates for cannabis-related offenses have decreased dramatically.

He emphasizes the need for better public education around cannabis, particularly regarding safe use practices and potential risks. Many dispensary workers lack formal training in cannabis pharmacology and effects, potentially leading to misinformation. Dr. Hill advocates for implementing educational requirements for cannabis retailers similar to alcohol server training programs.

Research Challenges and Future Directions

Studying the long-term effects of cannabis use presents several challenges. Unlike alcohol or tobacco, widespread cannabis use is a relatively recent phenomenon, making it difficult to assess lifelong impacts. Additionally, the increasing potency of cannabis over time complicates comparisons between older and newer studies.

Dr. Hill highlights several areas needing further research, including:

- The potential cardiovascular risks of long-term use

- The efficacy of cannabis for treating anxiety disorders and PTSD

- The mechanisms behind individual differences in cannabis response

- The clinical relevance of minor cannabinoids and terpenes

- Developing standardized dosing guidelines for medical use

He emphasizes the need for more placebo-controlled trials, particularly for CBD, to separate true pharmacological effects from expectancy.

Conclusion

Dr. Hill provides a balanced perspective on cannabis, acknowledging both its potential benefits and risks. He emphasizes that while cannabis is likely safer than some other recreational drugs, it is not without harm. Individual users must weigh the potential benefits against the risks, considering factors like age, mental health history, and pre-existing medical conditions.

He advocates for a public health approach focused on harm reduction rather than prohibition. This includes providing accurate information to users, implementing safety standards for cannabis products, and continuing research to better understand both the therapeutic potential and long-term health impacts of cannabis use.

The conversation between Dr. Hill and Andrew Huberman exemplifies how scientific disagreements can lead to productive dialogue and improved understanding. By openly discussing areas of uncertainty and conflicting evidence, they demonstrate the evolving nature of cannabis research and the importance of remaining open to new data.