Tetrahydrocannabinol (THC) is the primary psychoactive compound found in the cannabis plant. Its effects on the human body are mediated through the endocannabinoid system (ECS), a complex cell-signaling system identified in the early 1990s by researchers exploring THC. The ECS plays a role in regulating a range of functions and processes, including sleep, mood, appetite, memory, and fertility.

Mechanism of Action

THC primarily interacts with cannabinoid receptors in the ECS, particularly the CB1 and CB2 receptors.

CB1 Receptors

These receptors are most abundant in the brain and central nervous system (CNS), specifically in areas controlling:

• Movement and Coordination: Basal ganglia and cerebellum
• Memory: Hippocampus
• Cognition and Decision-making: Cerebral cortex
• Pain Modulation: Spinal cord

THC acts as a partial agonist to CB1 receptors, mimicking the action of naturally produced endocannabinoids like anandamide. This binding leads to the psychoactive effects associated with cannabis use.

CB2 Receptors

These receptors are mostly found in peripheral organs, especially cells associated with the immune system. When THC binds to CB2 receptors, it can influence inflammation and immune response.

Psychological and Cognitive Effects

The concentration of CB1 receptors in the brain dictates many of the psychological and cognitive effects of THC.

System	Effect	Duration
Central Nervous System	Euphoria, relaxation, altered sense of time	1–4 hours (inhalation)
Cognition	Impaired short-term memory, difficulty with concentration	Varies based on dose
Perception	Heightened sensory perception, changes in mood and thought

Physical and Physiological Effects

THC affects several physiological systems in the body.

Cardiovascular System

THC can cause acute cardiovascular changes, primarily due to its impact on the autonomic nervous system.

• Heart Rate: Tachycardia (increased heart rate) is a common, dose-dependent effect.
• Blood Pressure: Vasodilation can lead to a temporary decrease in blood pressure, potentially causing orthostatic hypotension (dizziness upon standing).

Respiratory System

The method of consumption significantly impacts the respiratory system.

• Inhalation (Smoking/Vaping): Irritation to the respiratory tract, cough, and potential for chronic bronchitis symptoms with heavy use.
• Edibles/Topicals: Minimal to no direct respiratory effect.

Digestive System

THC's interaction with the ECS in the gut and brain contributes to several digestive effects.

• Appetite Stimulation: Commonly referred to as "the munchies," THC stimulates appetite through hypothalamic CB1 receptor activation.
• Nausea/Vomiting: THC has antiemetic properties and is often used therapeutically to reduce nausea.

Potential Adverse Effects

While many effects are temporary, prolonged or high-dose use can lead to adverse outcomes.

• Impaired Motor Skills: Increased risk of accidents, making activities like driving unsafe.
• Psychiatric: Acute anxiety, paranoia, and, in susceptible individuals, an increased risk of psychosis.
• Cannabinoid Hyperemesis Syndrome (CHS): A rare condition involving cyclical episodes of severe nausea, vomiting, and abdominal pain, often relieved only by hot showers.