What is the endocannabinoid system?

The endocannabinoid system is a cell-signaling network found in humans and other animals. It has three parts: endocannabinoids, cannabinoid receptors, and enzymes that build and break down those endocannabinoids. Researchers named it after the plant compounds, called cannabinoids, that led to its discovery in the 1990s. THC from cannabis binds the same receptors. The system appears in the brain, spinal cord, immune cells, gut, skin, and liver.

endocannabinoid system for beginners

What the system does

The endocannabinoid system helps cells talk to each other. It takes part in appetite, sleep, pain signaling, mood, memory, immune response, and body temperature. Its signals travel backward compared with most signaling systems. Endocannabinoids are made in the receiving cell and travel to the sending cell, where they cut the release of other neurotransmitters. Scientists call this retrograde signaling.

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The three core parts

Endocannabinoids

Two endocannabinoids get the most study: anandamide and 2-arachidonoylglycerol, or 2-AG. Both are lipids made from fatty acids in cell membranes. Anandamide was found in 1992 by Raphael Mechoulam and colleagues. Its name comes from the Sanskrit word ananda, meaning bliss. 2-AG is the more abundant of the two in the brain. These molecules are made on demand and are not stored in vesicles like other neurotransmitters.

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Receptors

CB1 and CB2 are G protein-coupled receptors. CB1 was cloned in 1990. It sits in high numbers in the brain and central nervous system, and in lower numbers in the liver, fat tissue, and muscle. CB2 was cloned in 1993. It shows up on immune cells, in the spleen, and in the gut. THC binds both receptors as a partial agonist. CB1 is the receptor tied to the psychoactive effects of THC.

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Enzymes

FAAH breaks down anandamide into arachidonic acid and ethanolamine. MAGL breaks down 2-AG into arachidonic acid and glycerol. These enzymes control how long each signal lasts. Blocking FAAH raises anandamide levels in animal studies. Human trials of FAAH inhibitors stopped after liver damage and one death in a 2016 study in France.

How THC and CBD interact with the system

THC is a partial agonist at CB1 and CB2. It activates the same receptors that anandamide and 2-AG use, which is why it can affect appetite, memory, pain, and mood. CBD binds CB1 with low affinity. Lab work shows CBD acts as a negative allosteric modulator at CB1, meaning it changes the receptor shape and lowers the effect of THC. CBD also inhibits FAAH in test-tube studies and acts on serotonin 5-HT1A receptors.

What research has not settled

Studies of the human endocannabinoid system have limits. Researchers measure endocannabinoids in blood and spinal fluid, and those levels may not match levels in the brain. Small samples are common. Claims that cannabis balances the system or treats a specific condition need clinical trials. As of 2025, the FDA has approved cannabis-related drugs for nausea from chemotherapy, appetite loss in AIDS, and two rare forms of childhood epilepsy. The system itself remains a research target for pain, anxiety, and metabolic disease.