Cannabis gets its high by borrowing a system the body already has, one built around a receptor called CB1.1PubMed Central. Characterization and localization of cannabinoid receptors in rat brain: a quantitative in vitro autoradiographic study CB1 is among the most common receptors in the brain, and it also sits in the gut, liver and blood vessels, and even inside the cell structures that make energy.2PubMed Central. Cannabinoids and the gastrointestinal tract3PubMed. Functional Analysis of Mitochondrial CB1 Cannabinoid Receptors (mtCB1) in the Brain Its usual job is to turn things down rather than up, which is why a single receptor can touch mood, memory, pain and appetite all at once. It is also very old. Fish, birds and even sea squirts have it, so it predates humans by hundreds of millions of years.4u Bucha. Evolution of the Endocannabinoid System in Animals
The Body’s Own Keys and the Outside Ones
A receptor is a protein on the surface of a cell, waiting for a matching chemical. When the right molecule docks, the receptor passes a message into the cell. That is the lock-and-key picture: the receptor is the lock, and many different keys can fit it, each with a different effect. Some keys turn it fully, and others turn it only partway.
The body makes its own cannabis-like chemicals, called endocannabinoids, and the two main ones are anandamide and 2-AG.5PubMed Central. The Interplay of Exogenous Cannabinoid Use on Anandamide and 2-Arachidonoylglycerol in Anxiety: Results from a Quasi-Experimental Ad Libitum Study 2-AG is far more plentiful in the brain and switches CB1 on fully.6PubMed Central. The Interplay of Exogenous Cannabinoid Use on Anandamide and 2-Arachidonoylglycerol in Anxiety: Results from a Quasi-Experimental Ad Libitum Study Anandamide switches it on only partway, more like a dimmer than a light switch.7PubMed Central. The Interplay of Exogenous Cannabinoid Use on Anandamide and 2-Arachidonoylglycerol in Anxiety: Results from a Quasi-Experimental Ad Libitum Study
THC, the part of cannabis that causes the high, also switches CB1 on only partway.8PubMed Central. The Interplay of Exogenous Cannabinoid Use on Anandamide and 2-Arachidonoylglycerol in Anxiety: Results from a Quasi-Experimental Ad Libitum Study The high itself comes mainly from CB1 in the brain.9PubMed Central. Cannabinoid Receptor type 1 and its role as an analgesic: An opioid alternative? THC may also lower anandamide levels at nerve connections, more so at higher doses.10PubMed Central. The Interplay of Exogenous Cannabinoid Use on Anandamide and 2-Arachidonoylglycerol in Anxiety: Results from a Quasi-Experimental Ad Libitum Study CBD doesn’t switch CB1 on. It is thought to change the receptor’s shape so other keys work less well.11PubMed Central. The Interplay of Exogenous Cannabinoid Use on Anandamide and 2-Arachidonoylglycerol in Anxiety: Results from a Quasi-Experimental Ad Libitum Study
THC is not just “more endocannabinoid.” The body releases its own chemicals briefly and only where they’re needed. THC reaches receptors everywhere at once and stays for hours, which turns a subtle local brake into a strong, body-wide effect.
The same logic explains why one plant can feel so different from product to product. Because CBD doesn’t switch CB1 on, it doesn’t produce a high, which is why CBD on its own isn’t intoxicating the way THC is. The mix of the two in a product, and the dose, shapes how it feels. Both compounds also act on other receptors, so CB1 explains the high but not everything cannabis does.
What Happens Inside a Cell When CB1 Turns On
Once a key docks, CB1 hands its signal to helper proteins inside the cell.12PubMed Central. CB1 Cannabinoid Receptors and their Associated Proteins Those helpers lower the level of a messenger cells use to stay active.13PubMed Central. CB1 Receptor Signaling in the Brain: Extracting Specificity from Ubiquity They reduce the enzyme that makes it, so less of the messenger is around and the cell’s internal activity settles down.
The helpers also close channels that let calcium in and open channels that let potassium out, and both changes make a nerve cell less likely to fire.14PubMed Central. CB1 Cannabinoid Receptors and their Associated Proteins Calcium is what nerve endings need to release their chemical messages, so less calcium means fewer messages sent.
CB1 can also signal through a different helper, which pulls the receptor into the cell and out of action.15PubMed Central. CB1 Cannabinoid Receptor Signaling and Biased Signaling And CB1 can pair up with dopamine receptors; when it does, it changes which helper it uses.16PubMed. Concurrent stimulation of cannabinoid CB1 and dopamine D2 receptors enhances heterodimer formation: a mechanism for receptor cross-talk? That pairing helps explain cannabis’s links with reward and movement.
A Brake That Works Backwards in the Brain
Normally messages cross from a sending cell to a receiving cell, but endocannabinoids travel the other way.17PubMed Central. Endocannabinoid-mediated long-term plasticity requires cAMP/PKA signaling and RIM1alpha The receiving cell makes them when it is very active, and they reach CB1 on the sending cell’s endings.18PubMed Central. Endocannabinoid-mediated long-term plasticity requires cAMP/PKA signaling and RIM1alpha19PubMed. Postsynaptic endocannabinoid release is critical to long-term depression in the striatum The sender then releases fewer messages for a while.20PubMed Central. Retrograde endocannabinoid signaling in a postsynaptic neuron/synaptic bouton preparation from basolateral amygdala Blocking CB1 wipes out this effect, which shows the receptor is essential to it.21PubMed Central. Retrograde endocannabinoid signaling in a postsynaptic neuron/synaptic bouton preparation from basolateral amygdala The receiving cell makes endocannabinoids from fats in its own membrane, and the sender’s lowered release eases the strain on it.
This design is useful. It lets a receiving cell protect itself from being overloaded, and it acts only where activity is high, like a targeted dimmer. It can quiet both exciting and calming signals, so the overall effect depends on location. Cannabis disrupts the tidy arrangement by activating receptors everywhere.
The quieting can last seconds or become long-lasting.22PubMed Central. Endocannabinoid-mediated long-term plasticity requires cAMP/PKA signaling and RIM1alpha Long-lasting weakening of connections in movement circuits depends on CB1.23PubMed. Postsynaptic endocannabinoid release is critical to long-term depression in the striatum24PubMed Central. Cannabinoid CB1 receptor-dependent long-term depression in autaptic excitatory neurons That means CB1 helps the brain decide which connections to keep strong, a basis of learning.
Where CB1 Sits in the Brain and What That Explains
CB1 is packed most densely in movement areas deep in the brain and in the cerebellum, which coordinates movement.25PubMed Central. Characterization and localization of cannabinoid receptors in rat brain: a quantitative in vitro autoradiographic study It is also dense in the hippocampus, a memory centre, and in the smell centre.26PubMed Central. Characterization and localization of cannabinoid receptors in rat brain: a quantitative in vitro autoradiographic study These locations match cannabis’s effects on coordination and short-term memory.27PubMed Central. Characterization and localization of cannabinoid receptors in rat brain: a quantitative in vitro autoradiographic study
In daily life, the clumsiness and slow reactions after cannabis reflect receptors in the movement areas, which is why driving afterward is risky. Losing track of what you were saying reflects the hippocampus. The hippocampus helps form new memories and depends on well-timed signals between its cells. When THC activates CB1 there, it dampens the connections that help lay down new memories. Older, well-established memories are held elsewhere and are generally less affected than forming new ones.
CB1 is scarce in the brainstem areas that control breathing, which is why, unlike opioids, cannabis alone rarely stops breathing.
Stress, Fear and Memory
When a threat appears, anandamide drops, which releases a brake, helps switch on the body’s stress-hormone system and raises anxiety.28PubMed Central. Neurobiological Interactions Between Stress and the Endocannabinoid System Later, 2-AG rises and helps shut that system back down.29PubMed Central. Neurobiological Interactions Between Stress and the Endocannabinoid System CB1 in brain areas that control hormones is needed for stress hormones to turn off their own release.30PubMed Central. The endocannabinoid system in guarding against fear, anxiety and stress
Fear also has to be let go. Mice without CB1 learn fear normally but struggle to unlearn it when the danger is gone.31PubMed. The endogenous cannabinoid system controls extinction of aversive memories Blocking CB1 has the same effect, showing it matters at the moment of unlearning.32PubMed. The endogenous cannabinoid system controls extinction of aversive memories
Unlearning fear is new learning, not erasing. Fear fades when a once-dangerous cue repeatedly comes without harm. Trouble with this process is linked to anxiety and trauma-related problems, which is why CB1 is studied for those conditions, though human treatments aren’t established.
Pain Control
Pain messages arrive in the spinal cord from nerves in the body, then pass to relay cells that send them up to the brain. CB1 in the spinal cord sits on those relay cells and on the endings of the nerves bringing pain in.33PubMed Central. Activation of spinal and supraspinal cannabinoid-1 receptors lead to antinociception in a rat model of neuropathic spinal cord injury pain Activating it cuts the release of pain messages at the handoff and makes relay cells less likely to pass them along.34PubMed Central. Activation of spinal and supraspinal cannabinoid-1 receptors lead to antinociception in a rat model of neuropathic spinal cord injury pain
In rats with spinal cord injury, activating CB1 in the spinal cord or brain eased nerve pain.35PubMed Central. Activation of spinal and supraspinal cannabinoid-1 receptors lead to antinociception in a rat model of neuropathic spinal cord injury pain A midbrain pain-control area uses CB1 to reduce later, lasting pain but not the first sharp pain.36PubMed Central. Cannabinoid Receptor type 1 and its role as an analgesic: An opioid alternative?
The high comes from CB1 in the brain, while pain relief may come partly from CB1 in the spine and nerves. That is why drugs acting outside the brain are being pursued. Most of the evidence is from animals.
CB1 Beyond the Brain, Gut, Liver, Heart and Cell Power
Nerves in the gut wall carry CB1, including in humans.37PubMed Central. Cannabinoids and the gastrointestinal tract Activating it slows stomach emptying and movement through the intestines, and it reduces stomach acid.38PubMed Central. Cannabinoids and the gastrointestinal tract39PubMed Central. Effects of Cannabinoids on Intestinal Motility, Barrier Permeability, and Therapeutic Potential in Gastrointestinal Diseases Slowing can calm an overactive gut, which fits with cannabis being used for nausea. The same slowing can cause fullness or constipation-like effects in some people.
In the liver, CB1 switches on genes for making fat.40PubMed Central. Endocannabinoid activation at hepatic CB1 receptors stimulates fatty acid synthesis and contributes to diet-induced obesity41PubMed Central. Endocannabinoid System in Hepatic Glucose Metabolism, Fatty Liver Disease, and Cirrhosis In mice this contributes to weight gain on fatty diets,42PubMed Central. Endocannabinoid activation at hepatic CB1 receptors stimulates fatty acid synthesis and contributes to diet-induced obesity which is why CB1 features in obesity research.
CB1 in blood vessel walls makes them widen.43PubMed Central. Cannabinoids, the Heart of the Matter In animals it widens vessels in the heart and brain especially.44PubMed. Hemodynamic effects of cannabinoids: coronary and cerebral vasodilation mediated by cannabinoid CB(1) receptors Endocannabinoids can lower blood pressure and weaken heart pumping.45PubMed Central. Endocannabinoids Acting at Cannabinoid-1 Receptors Regulate Cardiovascular Function in Hypertension Vessel widening is thought to contribute to the red eyes and dizziness on standing that cannabis can cause.
CB1 also sits on the parts of cells that make energy, in brain and muscle.46PubMed. Functional Analysis of Mitochondrial CB1 Cannabinoid Receptors (mtCB1) in the Brain There it lowers energy production in nerve cells.47PubMed. Mitochondrial CB₁ receptors regulate neuronal energy metabolism
Why Regular Use Builds Tolerance
Tolerance comes mainly from losing CB1 receptors, not from the body clearing the drug faster.48PubMed Central. Cannabinoid tolerance relies on CB1 receptor ubiquitination by NEDD4L With regular use, CB1 is activated again and again, and the cell responds by moving receptors off its surface. Constant activation pulls receptors inside cells, and many are tagged and destroyed rather than recycled.49PubMed Central. Mechanisms of Cannabinoid Tolerance50PubMed Central. Cannabinoid tolerance relies on CB1 receptor ubiquitination by NEDD4L With fewer receptors available, the same dose produces a smaller response.
Brain scans show daily users have about 20% fewer CB1 receptors.51PubMed Central. Mechanisms of Cannabinoid Tolerance The loss is mainly in the outer thinking layers, not deep areas.52PubMed Central. Mechanisms of Cannabinoid Tolerance
The receptors come back. Levels recover after stopping, typically within about four weeks. A tolerance break works on that principle: pausing lets receptors rebuild.
Medicines That Target CB1
Rimonabant, a CB1 blocker, helped weight loss but was withdrawn in Europe in 2008 over depression and suicidal thoughts. CB1 helps end stress responses, and fully blocking it in the brain removes that brake.
Newer drugs aim to keep rimonabant’s benefits without those effects.53PubMed Central. Targeting the Endocannabinoid CB1 Receptor to Treat Body Weight Disorders: A Preclinical and Clinical Review of the Therapeutic Potential of Past and Present CB1 Drugs Blockers that stay out of the brain have helped obesity and diabetes problems in animal tests.54PubMed. The therapeutic potential of targeting the peripheral endocannabinoid/CB(1) receptor system Approved cannabis medicines, by contrast, are activators, used for nausea or appetite.
Drugs that adjust CB1 rather than simply switching it may prove safer.55PubMed. Translational potential of allosteric modulators targeting the cannabinoid CB(1) receptor None of these is yet an approved everyday treatment.