The living body maintains a steady internal state through a process known as homeostasis. This involves constantly monitoring and adjusting internal physical and chemical conditions, such as body temperature, fluid balance, and blood sugar levels, to keep them within a narrow, functional range. These adjustments ensure optimal functioning, even when the external environment changes. Marijuana introduces external chemical compounds that interfere with this delicate balancing act.
The cannabis plant contains over 100 active chemical compounds called cannabinoids, the two most studied being Delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD). THC is the primary psychoactive component, responsible for the characteristic “high” and most of the drug’s pharmacological actions. CBD is non-psychoactive and is associated with effects such as anti-inflammatory properties. Introducing these compounds disrupts the body’s established internal signaling, creating a push-and-pull effect on various homeostatic systems.
The Endocannabinoid System: The Body’s Internal Balancer
The underlying mechanism for marijuana’s effects is its interaction with the Endocannabinoid System (ECS), a complex internal network that serves as a master regulator of homeostasis. The ECS manages nearly all bodily functions, including sleep, mood, appetite, and immune response. It is composed of three main parts: endogenous cannabinoids (endocannabinoids), cannabinoid receptors, and the enzymes that synthesize and break them down.
Endocannabinoids, such as anandamide (AEA) and 2-arachidonoylglycerol (2-AG), are naturally produced by the body and act as chemical messengers. They are synthesized on demand and travel backward across the synapse to control the release of other neurotransmitters, functioning like a “dimmer switch” for the nervous system. Specific enzymes quickly degrade them once signaling is complete to prevent overstimulation.
The endocannabinoids bind to two main types of receptors: CB1 and CB2. CB1 receptors are highly concentrated in the brain and central nervous system, influencing functions like memory, coordination, and pain perception. CB2 receptors are mainly found in the immune system and peripheral organs, playing a role in inflammation and immune response.
THC, the main psychoactive component of marijuana, is a molecular mimic of the body’s natural endocannabinoids, particularly anandamide. THC binds directly to and activates CB1 receptors in the brain, hijacking the ECS’s signaling pathways. This intense, prolonged activation overwhelms the natural, transient signaling of endocannabinoids, disrupting the system’s normal feedback loops. CBD does not bind directly to these receptors but instead influences the ECS by slowing the breakdown of anandamide, indirectly supporting the body’s natural balance without causing a high.
Effects on Metabolic and Energy Homeostasis
Marijuana significantly interferes with metabolic homeostasis, most famously by stimulating appetite, a phenomenon known as “the munchies”. This acute effect is mediated by THC’s activation of CB1 receptors in the hypothalamus, a region of the brain that governs appetite. This activation promotes an increased desire for food and shifts the body’s mechanisms toward energy storage.
The mechanism involves an increase in the production of ghrelin, often called the “hunger hormone,” which stimulates appetite and food intake. Activation of CB1 receptors in peripheral tissues like the liver and fat cells promotes the formation of fat and reduces insulin responsiveness in muscle tissue. This acute shift favors the storage of energy and disrupts metabolic balance.
Paradoxically, despite appetite stimulation, chronic cannabis users often show a lower average Body Mass Index (BMI) and lower rates of obesity and diabetes compared to non-users. Research suggests that long-term cannabis use may lead to a complex alteration in metabolic function. Chronic use can suppress the normal spike in insulin concentrations that occurs after a meal, suggesting a more efficient processing of glucose. However, chronic use can also be associated with increased visceral fat and a specific type of insulin resistance in fat tissue, indicating a nuanced, tissue-specific effect on energy regulation.
Modulation of Cardiovascular and Thermoregulation
Cannabis use acutely impacts the cardiovascular system and the body’s ability to maintain a stable core temperature, both functions managed by the autonomic nervous system. The most common cardiovascular response to THC is an increase in heart rate (tachycardia) and a slight rise in resting blood pressure. This is caused by THC stimulating CB1 receptors, which leads to increased activation of the sympathetic nervous system.
A more pronounced homeostatic disruption is orthostatic hypotension, a sudden drop in blood pressure when moving from sitting or lying to standing. This effect results from the drug interfering with the body’s reflex to maintain blood flow to the brain against gravity. While cardiovascular effects often become less pronounced with repeated exposure as tolerance develops, they can pose a risk for individuals with pre-existing heart conditions due to the increased cardiac workload.
Regarding thermoregulation, THC affects the body’s ability to maintain a constant temperature through CB1 receptor activation in the central nervous system. In high doses, THC can cause hypothermia (a decrease in core body temperature). This cooling effect is due to the inhibition of metabolic processes, which reduces the body’s internal heat production. At typical doses, the effect may be minor, sometimes causing initial vasodilation—the widening of blood vessels—which creates a temporary feeling of warmth or flushing.