2-[(1R,6R)-3-methyl-6-(prop-1-en-2-yl)cyclohex-2-en-1-yl]-5-pentylbenzene-1,3-diol · cannabidiol · MW 314.47 g/mol · C₂₁H₃₀O₂ · CAS 13956-29-1 · ChEMBL190461
Cannabidiol. The principal non-intoxicating constituent of Cannabis sativa · same C₂₁H₃₀O₂ formula and shared resorcinol scaffold as THC, but an open, un-cyclized ring that fails to close the THC pyran — the one structural difference that abolishes CB1 orthosteric agonism. A promiscuous, low-potency, non-orthosteric polypharmacology drug: CB1 negative allosteric modulator, 5-HT1A agonist, TRPV1 desensitizer, GPR55 antagonist. Trade names: Epidiolex / Epidyolex.
CBD is the pharmacological anti-THC. It carries the identical molecular formula (C₂₁H₃₀O₂) and the same alkyl-resorcinol head, but where THC's monoterpene ring closes onto the phenol oxygen to form the tricyclic dibenzopyran, CBD's ring stays open — a freely rotating cyclohexene bearing a pendant hydroxyl. That single difference means CBD does not fit the CB1 orthosteric pocket as an agonist. There is no G-protein activation, no toggle-switch rotation, and therefore no intoxication. Instead, CBD works by touching many targets weakly and, at CB1, from a different site entirely.
CBD binds an allosteric pocket on CB1, distinct from the orthosteric groove THC uses. It lowers the affinity and efficacy of orthosteric agonists (THC, 2-AG, anandamide) and dampens β-arrestin recruitment — a NAM, not an agonist (Laprairie 2015). This is the molecular basis of CBD blunting THC-induced anxiety and tachycardia.
CBD is a functional agonist at the Gi/o-coupled 5-HT1A receptor. This — not any cannabinoid receptor — likely carries its anxiolytic, anti-nausea and neuroprotective actions (blocked by the 5-HT1A antagonist WAY-100635 in animal models). Micromolar potency, but 5-HT1A-dependent behaviourally.
CBD activates the TRPV1 capsaicin channel (EC₅₀ ~1 µM) and, like capsaicin, drives it into desensitization — depleting the excitable Ca²⁺-permeable channel pool. Contributes to analgesic and anti-inflammatory effects and to calcium-dependent neuronal quieting.
CBD is an antagonist at GPR55 (the "CB3" orphan LPI receptor), IC₅₀ sub-µM. GPR55 raises intracellular Ca²⁺ and neuronal excitability; blocking it is a leading candidate mechanism for CBD's anticonvulsant action, independent of CB1.
CBD competes at intracellular fatty-acid-binding proteins (FABP5/7) that ferry anandamide to its degrading enzyme FAAH. By occupying the carrier, CBD raises endogenous anandamide — an indirect, "entourage-like" boost of endocannabinoid tone without ever agonizing CB1 itself.
CBD inhibits the equilibrative nucleoside transporter ENT1 (Ki ~250 nM), raising extracellular adenosine (anti-inflammatory, A1-mediated seizure-dampening), and is a PPARγ agonist driving nuclear anti-inflammatory transcription. Also modulates T-type Ca²⁺ channels and Nav currents at higher concentrations.
The honest summary: CBD has no single high-affinity target. Nearly every action is low-micromolar and the clinical effect is the sum of many weak, non-intoxicating pushes — the mechanistic opposite of THC's single dominant CB1 agonism. It reaches CB1 only obliquely, as a NAM, which is precisely why a person can take hundreds of milligrams and remain fully sober.
CBD is extremely lipophilic (logP ≈ 5.9) and suffers heavy hepatic first-pass, so oral bioavailability is a dismal ~6% in the fasted state. It is dramatically food-dependent: a high-fat meal raises Cmax roughly 4–5-fold — a genuine dosing hazard for a supposedly "gentle" molecule, because a fed Epidiolex dose is a different drug from a fasted one. The metabolic sting is not CBD's own clearance but what CBD does to other drugs: it is a potent inhibitor of CYP2C19, CYP3A4, CYP2C9 and UGT enzymes.
Metabolism cascade: hepatic CYP2C19 (> CYP3A4) hydroxylates CBD at C7 to an active metabolite, then oxidation and glucuronidation clear it. The active 7-OH is the reason genetics and interactions matter.
7-hydroxy-CBD (7-OH-CBD, marked ★) is pharmacologically active and circulates at meaningful concentrations, so CYP2C19 poor metabolizers (and patients on CYP2C19 inhibitors) run higher exposure. The clinically decisive interaction runs the other way: CBD inhibits CYP2C19, which is the enzyme that clears N-desmethylclobazam — the active metabolite of the anticonvulsant clobazam. Co-administration therefore raises active clobazam levels several-fold, producing sedation that is often mistaken for a CBD effect but is really a pharmacokinetic collision. CBD also raises exposure to other CYP substrates (tacrolimus, warfarin, some SSRIs) and, with valproate, produces dose-dependent transaminase elevations (a pharmacodynamic hepatotoxic interaction, not simple enzyme competition).
In June 2018 CBD became the first cannabis-derived molecule approved by the FDA — as Epidiolex, a purified plant-derived oral solution — for seizures in Dravet syndrome and Lennox–Gastaut syndrome, later extended to seizures in tuberous sclerosis complex. Randomized trials showed genuine, placebo-beating reductions in convulsive seizure frequency. Notably, the mechanism is not fully settled and is not CB1-mediated — a rare case of an approved drug whose target list is a committee.
GPR55 signaling raises presynaptic Ca²⁺ and glutamate release. CBD's GPR55 blockade lowers excitatory drive and is one of the leading candidate anticonvulsant mechanisms — entirely separate from the endocannabinoid CB1/CB2 axis.
By inhibiting the ENT1 adenosine reuptake transporter, CBD raises extracellular adenosine, which acts at inhibitory A1 receptors to suppress excitatory transmission — an endogenous "brake" that is also anti-inflammatory.
Sustained CBD desensitizes TRPV1, reducing the pool of Ca²⁺-permeable channels available to feed pathological hyperexcitability, and contributing to analgesia. A modulatory, use-dependent effect rather than simple block.
The behaviourally validated 5-HT1A agonism underlies CBD's separate reputation as an anxiolytic (acute social-anxiety trials), anti-emetic and neuroprotectant. This is the target most cleanly linked to the "calm without a high" that draws consumers to unregulated CBD products.
The through-line is weak affinity, broad reach, zero intoxication. Where THC's story is a single potent CB1 agonism with a soft ceiling, CBD's is a fistful of micromolar interactions that never once open the CB1 G-protein cavity. That is why the honest hero fact is "CB1 Ki ~4.4 µM (weak)" and the honest headline is "non-intoxicating" — and why the real risks live in the drug-interaction and product-quality columns, not in acute toxicity.
Evidence-based, non-moralistic. CBD is remarkably safe acutely — no known lethal dose, no intoxication, no meaningful abuse potential. The real hazards are almost entirely pharmacokinetic drug interactions (via CYP/UGT inhibition) and the lawless quality of unregulated products, not the molecule itself.
| Target | Affinity | Rel. | Mechanism |
|---|---|---|---|
|
CB1
Cannabinoid receptor 1 (CNR1)
|
Ki ≈ 4.35 µM
weak; range 1.5–>10 µM
|
Neg. allosteric mod. | |
|
CB2
Cannabinoid receptor 2 (CNR2)
|
Ki ≈ 2.86 µM
weak partial/inverse
|
Weak / inverse | |
|
5-HT1A
Serotonin 1A receptor (HTR1A)
|
agonist (µM)
functional; WAY-sensitive
|
Agonist | |
|
GPR55
Orphan LPI receptor ("CB3")
|
IC₅₀ ~0.4 µM
anticonvulsant candidate
|
Antagonist | |
|
TRPV1
Vanilloid / capsaicin channel
|
EC₅₀ ~1 µM
activate → desensitize
|
Agonist/desens. | |
|
ENT1
Equilibrative nucleoside transporter 1
|
Ki ≈ 250 nM
↑ adenosine
|
Inhibitor | |
|
CYP2C19
Cytochrome P450 2C19 (interaction)
|
Ki ≈ 0.79 µM
raises clobazam
|
Inhibitor |
CBD's targets are almost all low-micromolar — and that weakness is thermodynamically informative. Like THC, CBD buries a greasy, near-desolvated scaffold and gains a favourable hydrophobic solvent-entropy release (positive ΔSsolv). But CBD's open, freely rotating cyclohexene ring carries far more residual torsional freedom than THC's locked tricycle. On binding, that flexibility must be paid down as a large negative conformational-entropy term (ΔSconf < 0), and no single pocket recovers enough enthalpy to offset it — the molecular reason affinity stays micromolar everywhere.
At CB1 the contrast with THC is sharpest. THC's rigid ligand collapses the receptor's microstate distribution toward the active, G-protein-coupled ensemble — the Shannon-entropy narrowing that is agonism. CBD, binding an allosteric site, does the opposite: it reshapes rather than collapses the ensemble, raising the free-energy cost of reaching the active state for orthosteric agonists. In FlexAID∆S terms the tENCoM vibrational signature is not deep active-state rigidification but a redistribution of conformational entropy that disfavours transducer coupling — negative allosteric modulation as an entropic penalty, not an activating collapse.
The take-home: THC wins with one rigid, high-affinity, entropy-collapsing agonism; CBD works by many soft, entropy-expensive, non-collapsing touches. Same formula, opposite thermodynamics — and the reason one intoxicates and one does not.