The system you already have, mapped.

Cerebral cortex

The outer sheet of the brain, where deliberate thought, perception and judgement are organised.

• CB1 receptorrank 0.80●human · autoradiographyWidespread across the cortex, heaviest in frontal regions — judgement, planning and the sense of time.
• FAAHrank 0.80●human · immunohistochemistryFAAH is abundant on the receiving side of the synapse, destroying anandamide within seconds of its release.
• MAGLrank 0.80●human · immunohistochemistryMAGL sits on the *sending* side, which is the elegant part: 2-AG travels backwards across the synapse and is destroyed at the terminal it was aimed at.
• 5-HT1A receptorrank 0.70●human · autoradiographyWidespread cortical expression.
• CB2 receptorrank 0.12◗rodent · mrnaSparse, largely on microglia rather than neurons, and rising under inflammation.

Hippocampus

A pair of curved structures deep in the temporal lobes, central to laying down new memories.

• CB1 receptorrank 0.90●human · autoradiographyHigh density, and the direct explanation for the effect on forming new memories while intoxicated.
• 5-HT1A receptorrank 0.80●human · autoradiographyHigh density. This receptor is on the map because cannabidiol acts at it, not because it belongs to the cannabinoid system.
• FAAHrank 0.80●human · immunohistochemistryHigh, matching the density of the signalling it terminates.
• MAGLrank 0.70●human · immunohistochemistryHigh.

Cerebellum

The dense structure at the back and base of the brain, coordinating movement and balance.

• CB1 receptorrank 0.90●human · autoradiographyVery high density. Coordination and timing are cerebellar functions, and both are measurably affected.
• MAGLrank 0.80●human · immunohistochemistryHigh, alongside the CB1 it regulates.
• FAAHrank 0.70●human · immunohistochemistryHigh in the cerebellum.

Gut and enteric nervous system

The digestive tract and its own nerve net — enough neurons to be called a second brain, and it behaves like one.

• CB2 receptorrank 0.50●human · immunohistochemistryOn gut immune tissue, and upregulated where there is inflammation.
• CB1 receptorrank 0.40●human · immunohistochemistryOn enteric neurons, slowing motility — the same mechanism behind both the appetite change and the constipation.
• TRPV1 channelrank 0.40◗human · immunohistochemistryOn gut sensory fibres, relevant to visceral pain.
• FAAHrank 0.40◗human · mrnaPresent in the gut wall.

Liver

The body's chemical works: most of what is swallowed is processed here before it reaches the rest of you.

• FAAHrank 0.60●human · mrnaSubstantial — the liver clears endocannabinoids as it clears much else.
• MAGLrank 0.40◗human · mrnaModerate.
• CB1 receptorrank 0.20◗human · mrnaLow but functionally real, with a role in lipid handling.
• CB2 receptorrank 0.20◗human · mrnaLow at rest and rising with injury: this receptor turns up where there is damage.

Peripheral nerves

The nerves running out to the limbs and organs — where sensation arrives and movement leaves.

• TRPV1 channelrank 0.90●human · immunohistochemistryDense on sensory nerve endings. This is the channel that answers to chilli heat, and anandamide acts at it too.
• CB1 receptorrank 0.35●human · immunohistochemistryOn peripheral nerve terminals, which is part of why effects are not purely central.

Amygdala

Paired almond-shaped nuclei involved in threat appraisal and emotional salience.

• CB1 receptorrank 0.60●human · autoradiographyModerate density in the threat-appraisal circuitry. Relevant to why the same dose can calm one person and frighten another.
• 5-HT1A receptorrank 0.60●human · autoradiographyPresent in the threat circuitry, and the most plausible route for an anxiolytic effect that does not go through CB1 at all.

Skin

The largest organ, and the boundary — nerve endings, immune cells and glands all in one sheet.

• TRPV1 channelrank 0.60●human · immunohistochemistryIn the skin's sensory endings and keratinocytes.
• CB2 receptorrank 0.35◗human · immunohistochemistryOn skin immune cells, which is the basis of most topical claims — and the reason those claims are about the skin rather than the whole body.
• CB1 receptorrank 0.25◗human · immunohistochemistryIn nerve fibres, glands and keratinocytes. The largest organ is not exempt from the system.

Spinal cord

The main cable between brain and body, and the first place pain signals are gated.

• TRPV1 channelrank 0.70●human · immunohistochemistryOn incoming pain fibres at the dorsal horn.
• CB1 receptorrank 0.40●human · autoradiographyPresent in the dorsal horn, where incoming pain signals are first gated.

Basal ganglia

Deep nuclei — including the globus pallidus and substantia nigra — that shape movement and habit.

• CB1 receptorrank 1.00●human · autoradiographyThe densest CB1 territory in the brain — globus pallidus and substantia nigra especially, which is why movement is among the first things cannabis alters.

Spleen

An immune organ behind the stomach, dense with the white cells that patrol the blood.

• CB2 receptorrank 1.00●human · mrnaThe densest CB2 tissue. The receptor was found by looking in the periphery precisely because it is so abundant here.

Brainstem

The stalk joining brain to spinal cord. It runs breathing and heart rate without asking.

• 5-HT1A receptorrank 0.70●human · autoradiographyDense in the raphe nuclei, the brainstem's own serotonin source — one of the few places on this map where the brainstem is bright.
• CB2 receptorrank 0.15◗rodent · functionalCB2 in the brain was denied for years and is now accepted, chiefly on microglia. How much is there, and when, is still argued — so it is drawn as the uncertain thing it is.
• CB1 receptorrank 0.10●human · autoradiographyStrikingly sparse. The brainstem runs breathing, and the near-absence of CB1 here is why cannabis does not suppress respiration the way opioids do. It is not a claim that cannabis is harmless — the harms are real and are elsewhere.

Circulating immune cells

White cells moving through blood and lymph, so this one has no fixed address — it is everywhere at once.

• CB2 receptorrank 0.95●human · mrnaOn leukocytes throughout blood and lymph — which is why this row has no fixed address on the figure. Immune cells are not in a place.

Adipose tissue

Body fat, which is not inert storage but an active endocrine tissue.

• MAGLrank 0.50◗human · mrnaPresent in fat tissue, where MAGL also participates in ordinary lipid handling — a reminder that these enzymes had other jobs before we named them after cannabis.
• CB1 receptorrank 0.30◗human · mrnaPresent in fat tissue, where the system participates in energy balance rather than merely reflecting it.

Bone and marrow

The skeleton and the marrow inside it, where blood and immune cells are made.

• CB2 receptorrank 0.60●human · mrnaWhere immune cells are made, and where bone itself is remodelled.

Hypothalamus

A small central hub governing appetite, temperature, sleep and hormone release.

• CB1 receptorrank 0.45●human · autoradiographyModerate, and the appetite effect lives partly here.

Reproductive tissue

The gonads and associated tissue, which carry the system in both sexes.

• CB1 receptorrank 0.30◗human · mrnaPresent in reproductive tissue, with roles in fertility that are still being characterised.

Heart and vessels

The pump and the pipework, including the vessel walls that set blood pressure.

• CB1 receptorrank 0.20◗human · functionalIn the heart and vessel walls, contributing to blood-pressure regulation.

Lungs

Where breath meets blood — and, for anything inhaled, the first tissue it touches.

• CB1 receptorrank 0.15◗human · mrnaLow. Worth noticing that the tissue most exposed by smoking is not the tissue most receptive to the drug.

Δ9-tetrahydrocannabinol, the plant molecule responsible for intoxication. A partial agonist at CB1 — it turns the receptor on, but not fully.

Usually got wrong — THC is a partial agonist, not a full one. That single fact is why the receptor's own messengers can be displaced by it, and part of why tolerance builds the way it does.

• CB1 receptorpartial agonist · up●humanThe interaction that makes cannabis cannabis. Partial rather than full agonism: it turns CB1 on, but never as hard as the receptor can go.
• CB2 receptorpartial agonist · up●humanTHC acts at CB2 as well. Because CB2 sits on immune cells rather than neurons, this arm of its activity is not what is felt.

Cannabidiol. Not intoxicating, and — this is the part that surprises people — barely active at CB1 at all.

Usually got wrong — CBD is not 'the calm one at the same receptor'. Its affinity for CB1 is very low; what it does happens largely elsewhere. Watch how little of the gold lights up, and where the map moves instead.

• CB1 receptornegative allosteric · down●in-vitroNot an agonist. Cannabidiol binds CB1 at a different site and changes how *other* things act there — which is close to the opposite of what it is usually said to do, and is why the gold barely lifts.
• TRPV1 channelagonist · up◗in-vitroCannabidiol activates the vanilloid channel — the chilli-heat receptor. A large part of what it does happens on nerve endings, not in the brain's cannabinoid system.
• 5-HT1A receptoragonist · up◗in-vitroActivity at a serotonin receptor. If cannabidiol calms anything, this is a more plausible route than CB1 — and it is a serotonergic story, not a cannabinoid one.
• FAAHenzyme inhibitor · up◗in-vitroSlowing the enzyme that destroys anandamide raises your own anandamide. Note the direction: the signal goes *up* because its off-switch was slowed.

One of the two messengers your body makes for this system. Named from ānanda, the Sanskrit for bliss — an unusually candid piece of naming for a molecule.

Usually got wrong — It is made on demand and destroyed within seconds by FAAH, never stored. Your own signalling is local and brief; an inhaled agonist is neither.

• CB1 receptorpartial agonist · up●humanThe endogenous ligand CB1 was found to have. Made on demand, acting locally, gone in seconds.
• TRPV1 channelagonist · up◗in-vitroAnandamide also acts at TRPV1, which is why the body's own cannabinoid is not a tidy one-receptor molecule either.
• FAAHenzyme inhibitor · down●humanShown here as the relationship it is: FAAH is what ends anandamide. Where FAAH is dense, anandamide is brief.

The other endogenous messenger, and the more abundant of the two. Ended by MAGL rather than FAAH.

Usually got wrong — Two messengers with two different off-switches is not redundancy — they are released in different circumstances and reach different distances.

• CB1 receptoragonist · up●humanThe more abundant of the two endogenous messengers, and a full agonist where anandamide is partial.
• CB2 receptoragonist · up●humanActive at CB2 as well, which is part of how the immune arm of the system is spoken to from inside.
• MAGLenzyme inhibitor · down●humanMAGL is 2-AG's off-switch, sitting on the terminal the signal was aimed at.

Sustained aerobic effort raises circulating endocannabinoids. Not a molecule you take — a state you can put yourself in.

Usually got wrong — The 'runner's high' was attributed to endorphins for decades. Endorphins are large molecules that cross into the brain poorly; endocannabinoids do not have that problem.

• CB1 receptorraises endogenous · up◗humanSustained aerobic effort raises circulating endocannabinoids in humans. Not a molecule taken — a state entered, acting through the system already there.
• CB2 receptorraises endogenous · up○rodentThe 'runner's high' was shown to depend on cannabinoid receptors — in mice. Real, suggestive, and not a human result, so it is drawn as the haze it is.