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Research tools

O-1918

Reference antagonist of the endothelial abnormal-cannabidiol receptor, a laboratory tool of debated selectivity.

Unscheduled
Level of detail

Harm-reduction warning

No characterised human dose: animal / in vitro data only. Effect profile, safety margin and acute toxicity are not documented in human clinical practice. Extremely potent compound: severe effects, seizures and deaths reported in the literature.

C₁₉H₂₆O₂

CAS 536697-79-7

Family
ECS pharmacological toolOther target
Molar mass
286.40 g/mol

Updated on

In plain terms

O-1918 is not a consumer product: it is a laboratory reagent, a chemical cousin of cannabidiol. Researchers use it to block certain receptors and check that an observed effect really goes through them; its selectivity is however debated, since it also acts on potassium channels. It does not exist in hemp.

Receptors and activity

Target network

CB1 / CB2Binding (function not established)no measured value
  • Blocks or inhibits
  • Binds or modulates

The lower the cited value, the closer the target sits to O-1918: one ring per factor of 100. A target with no measured value stays on the edge.

Where these targets live

Where each target has been found in humans, according to the cited studies. The map shows the target, not an effect of O-1918.

Brain, side view
Body, front view
Blood

CB1CB1 found in 7 regions of the body

  1. Basal gangliadenseMost dense in basal ganglia outflow nuclei1
  2. CerebellumdenseVery dense in the cerebellum1
  3. HippocampusdenseVery high concentrations in the hippocampus2
  4. AmygdaladenseHigh concentrations in the amygdala2
  5. CortexpresentPresent throughout the neocortex2
  6. Adipose tissuepresentExpressed in adipose tissue3
  7. GutpresentColonic epithelium, smooth muscle and plexus4

Map sources

  1. Herkenham M et al. Cannabinoid receptor localization in brain. Proc Natl Acad Sci U S A, 1990 (new tab)
  2. Glass M et al. Cannabinoid receptors in the human brain: a detailed anatomical and quantitative autoradiographic study in the fetal, neonatal and adult human brain. Neuroscience, 1997 (new tab)
  3. Engeli S et al. Activation of the peripheral endocannabinoid system in human obesity. Diabetes, 2005 (new tab)
  4. Wright K et al. Differential expression of cannabinoid receptors in the human colon: cannabinoids promote epithelial wound healing. Gastroenterology, 2005 (new tab)

Cited values

  1. Abnormal-cannabidiol endothelial receptorAntagonistno measured value cited
  2. GPR18Antagonistno measured value cited
  3. BKCa potassium channelsInhibitorIC50 = 257 nM43 out of 100

    Godlewski et al., J Pharmacol Exp Ther 2009 (new tab) · inhibition of the BKCa current, pIC50 6.59 converted to nM

  4. CB1 / CB2Binding (function not established)no measured value cited
Bar length follows the measured value (Ki, Kd, EC50 or IC50), on one scale shared by every entry, from 100 µM to 0.1 nM. A target with no cited value has no bar.

Pharmacology

O-1918 is a synthetic analogue of cannabidiol in which both phenol groups are methylated and the pentyl chain is replaced by a methyl. Offertáler et al. (2003) described it as a silent antagonist of an endothelial receptor coupled to Gi/Go and to the PI3 kinase/Akt pathway, distinct from CB1 and CB2: with no binding to these two receptors and no vasorelaxation of its own up to 30 µM, it inhibits in a concentration-dependent manner (1 to 30 µM) the relaxation of rat mesenteric artery by abnormal cannabidiol and anandamide. This reading has since been qualified. GPR55 is ruled out of the vascular mechanism (Kb of 1.8 and 2.8 µM in wild-type and GPR55-/- mice; Johns et al. 2007); GPR18 is a candidate, with O-1918 blocking the fall in intraocular pressure induced by abnormal cannabidiol and N-arachidonoylglycine in mice (Caldwell et al. 2013) but itself behaving as an agonist of the calcium and ERK1/2 pathways of GPR18-expressing cells (Console-Bram et al. 2014); and it directly inhibits BKCa channels (pIC50 of 6.59; Godlewski et al. 2009) and, according to the review by Bondarenko et al. (2018), the Na+/Ca2+ exchanger, which calls for caution when reading studies based on its sensitivity alone. In anaesthetised rats, 3 µmol/kg O-1918 reduced the delayed vascular effects of anandamide by 30 to 70% (Zakrzeska et al. 2010). All these data are preclinical.

Key sources.

History

Source
A synthetic molecule, a cannabidiol analogue (dimethyl ether), absent from cannabis and from any living organism. A research reagent.

Origin

Research tool

No natural biosynthetic pathway: the molecule is formed in no living organism and has not been reported in hemp. It is a synthetic compound, the dimethyl ether of a terpenylated resorcinol of the cannabidiol type.

Classification

Family, origin and source verification

Family

ECS pharmacological tool › Other target

Verification

Classification, sources and binding values checked on 20 October 2026; text read against its sources and Wikipedia.

Wikipedia (English)

O-1918 (new tab)

Article paired by the molecule's structure (InChIKey), revision read on 19 October 2026. Read as a second opinion, never cited as a source.

References

  1. Offertáler L, Mo FM, Bátkai S et al., Selective ligands and cellular effectors of a G protein-coupled endothelial cannabinoid receptor, Mol Pharmacol 2003 (new tab)PMID 12606780
  2. Johns DG et al., The novel endocannabinoid receptor GPR55 is activated by atypical cannabinoids but does not mediate their vasodilator effects, Br J Pharmacol 2007 (new tab)PMID 17704827
  3. Caldwell MD et al., A GPR18-based signalling system regulates IOP in murine eye, Br J Pharmacol 2013 (new tab)PMID 23461720
  4. Console-Bram L et al., Activation of GPR18 by cannabinoid compounds: a tale of biased agonism, Br J Pharmacol 2014 (new tab)PMID 24762058
  5. Godlewski G et al., The endogenous brain constituent N-arachidonoyl L-serine is an activator of large conductance Ca2+-activated K+ channels, J Pharmacol Exp Ther 2009 (new tab)PMID 18923087
  6. Bondarenko AI et al., The quest for endothelial atypical cannabinoid receptor: BKCa channels act as cellular sensors for cannabinoids in in vitro and in situ endothelial cells, Vascul Pharmacol 2018 (new tab)PMID 29355732
  7. Zakrzeska A et al., A cannabinoid receptor, sensitive to O-1918, is involved in the delayed hypotension induced by anandamide in anaesthetized rats, Br J Pharmacol 2010 (new tab)PMID 20105178
  8. ANSM, consolidated list of substances classified as narcotics, updated 16 February 2026, annex IV (benzo[c]chromene heading) (new tab)
  9. PubChem, Compound Summary CID 40469923, O-1918 (new tab)

Identifiers

Names

IUPAC name
1,3-dimethoxy-5-methyl-2-[(1R,6R)-3-methyl-6-prop-1-en-2-ylcyclohex-2-en-1-yl]benzene
Other names
O 1918 · O1918

Identifiers

Formula
C₁₉H₂₆O₂
CAS
536697-79-7
PubChem CID
40469923(new tab)
InChIKey
ICHJMVMWPKLUKT-JKSUJKDBSA-N
SMILES
CC1=C[C@H]([C@@H](CC1)C(=C)C)C2=C(C=C(C=C2OC)C)OC

Machine-readable entry (JSON)

LLM ingestion format: a structured superset of the entry (identifiers, binding, versioned legal status). Full corpus.