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Research tools

Otenabant

Pfizer's anti-obesity CB1 blocker, halted in phase 3 over psychiatric risk.

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.

C₂₅H₂₅Cl₂N₇O

CAS 686344-29-6

Family
ECS pharmacological toolAntagonist or inverse agonist
Molar mass
510.40 g/mol

Updated on

In plain terms

Otenabant is an experimental medicine developed by the pharmaceutical company Pfizer against obesity. Instead of imitating cannabinoids, it does the opposite: it blocks the CB1 receptor, the one THC activates. In clinical trials it led to weight loss, but symptoms of anxiety and depression and suicidal thoughts were reported more often than on placebo; the programme was stopped before completion.

Receptors and activity

Target network

CB1Inverse agonistKi = 0.7 nM · humanbinding; 0.12 nM in functional assay (Griffith 2009)
  • Blocks or inhibits
  • Binds or modulates

The lower the cited value, the closer the target sits to Otenabant: 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 Otenabant.

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. CB1Inverse agonistKi = 0.7 nM · human86 out of 100

    Hadcock et al., Biochem Biophys Res Commun 2010 (new tab) · binding; 0.12 nM in functional assay (Griffith 2009)

  2. CB2Binding (function not established)Ki = 7.6 µM · human19 out of 100

    Hadcock et al., Biochem Biophys Res Commun 2010 (new tab) · binding (approximately 10,000-fold selectivity for CB1)

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

Otenabant is a competitive antagonist and inverse agonist of the CB1 receptor, from a series of 8,9-diarylpurines developed at Pfizer. Its affinity for human CB1 is subnanomolar (Ki of 0.7 nM in binding, 0.12 nM in a functional assay) against 7,600 nM for CB2 (Griffith et al. 2009; Hadcock et al. 2010). In animals it reverses the four central responses caused by a synthetic cannabinoid agonist (reduced motor activity, hypothermia, analgesia, catalepsy), reduces food intake and increases energy expenditure and fat oxidation (Hadcock et al. 2010). In humans, three phase 3 trials (10 and 20 mg a day; 1,253, 2,536 and 975 participants) showed dose-related weight loss after one year of treatment, but self-reported anxiety, suicidal thoughts, depression and depressed mood were more frequent than on placebo, without a consistent dose-effect relation; the two two-year trials and the programme were stopped before completion because of the changing position of regulators on drugs acting on CB1 (Aronne et al., Obesity 2011, PMID 21293451). No therapeutic benefit is established.

Key sources.

History

Source
A pharmaceutical laboratory molecule, designed at Pfizer as a candidate medicine against obesity and type 2 diabetes, then abandoned. It occurs in no plant and is found in no consumer product: hemp contains none of it, and otenabant has never been marketed in any form whatsoever. Its use remains strictly experimental.

Origin

Research tool

No biosynthetic pathway: otenabant is an entirely synthetic molecule, arising from a series of diarylpurines developed in medicinal chemistry. No living organism, plant or animal, produces it, and it derives from no natural cannabinoid precursor.

Classification

Family, origin and source verification

Family

ECS pharmacological tool › Antagonist or inverse agonist

Verification

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

Wikipedia (English)

Otenabant (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. Griffith DA et al., J Med Chem 2009: discovery of CP-945,598 (new tab)PMID 19102698
  2. Hadcock JR et al., Biochem Biophys Res Commun 2010: in vitro and in vivo pharmacology of CP-945,598 (new tab)PMID 20211605
  3. Aronne LJ et al., Obesity 2011: efficacy and safety of CP-945,598 (phase 3 trials) (new tab)PMID 21293451
  4. Miao Z et al., Drug Metab Dispos 2012: excretion, metabolism and pharmacokinetics in healthy volunteers (new tab)PMID 22187487
  5. Miao Z et al., Drug Metab Dispos 2011: excretion, metabolism and pharmacokinetics in rats, mice and dogs (new tab)PMID 21875952
  6. Tseng E et al., Drug Metab Dispos 2014: relative contributions of CYP3A4 and CYP3A5 (new tab)PMID 24737844
  7. PubChem, compound CID 10052040 (otenabant) (new tab)

Identifiers

Names

IUPAC name
1-[8-(2-chlorophenyl)-9-(4-chlorophenyl)purin-6-yl]-4-(ethylamino)piperidine-4-carboxamide
Other names
CP-945598 · CP-945,598

Identifiers

Formula
C₂₅H₂₅Cl₂N₇O
CAS
686344-29-6
PubChem CID
10052040(new tab)
InChIKey
UNAZAADNBYXMIV-UHFFFAOYSA-N
SMILES
CCNC1(CCN(CC1)C2=NC=NC3=C2N=C(N3C4=CC=C(C=C4)Cl)C5=CC=CC=C5Cl)C(=O)N

Machine-readable entry (JSON)

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