RESEARCH MONOGRAPH · KDC-MN-328

URB597

May 9, 2026 Kodiac biolabs Research Revised May 30, 2026 3 min read

Our opinion on this compound

73/100

The classic FAAH inhibitor, foundational tool, mostly superseded by better-characterized alternatives for in vivo work

URB597 (also called KDS-4103 in some older papers) is the irreversible FAAH inhibitor that essentially opened up the FAAH-as-target field. Piomelli and Tarzia synthesized it, the 2003 J Med Chem paper established the carbamate-based mechanism (covalent acylation of the FAAH catalytic serine), and from there it became the workhorse for any in vivo experiment that wanted to elevate endogenous anandamide tone without administering anandamide directly.

Mechanism is well-mapped: covalent FAAH inhibitor, IC50 in the low nM range, selectivity over other serine hydrolases is reasonable but not perfect (some MAGL crossreactivity at higher concentrations, plus the carboxylesterase issue that bedevils carbamates generally). In vivo it produces 2-10x elevations in brain anandamide concentrations and downstream behavioral effects: anxiolysis, antinociception, antidepressant-like signals in rodent models.

The interesting thing about FAAH inhibition mechanistically is that it doesn't produce the THC-like effects you'd predict from a direct CB1 agonist, even though it raises anandamide tone substantially. The on-demand nature of endocannabinoid signaling means you're amplifying endogenous tone where it's already active rather than activating CB1 everywhere uniformly. Thats the whole therapeutic appeal of the target class.

For research URB597 has been used in literally thousands of papers. Anxiety models, depression models, addiction work, pain work. The phenotype is reproducible across groups. The main caveats are the carboxylesterase off-target activity in rodents (Pinto and colleagues documented this, makes high-dose interpretation messier) and the irreversibility (covers fresh FAAH protein synthesis is the off-mechanism, so PD is determined by enzyme resynthesis rates rather than drug PK).

Sourcing: synthetic URB597 is widely available from research-chemical suppliers, purity by HPLC and ideally LCMS, the carbamate chemistry is straightforward to verify. Cost is modest for a research compound. Solubility is lousy in water (you're dissolving in DMSO/cremophor/saline mixes for in vivo).

What we like: foundational FAAH inhibitor, mechanism is textbook, behavioral phenotype is well-characterized, useful for endocannabinoid biology.

What we dont like: the off-target carboxylesterase activity, and the fact that PF-04457845 is a cleaner more potent alternative for any modern work where you have the choice.

Historical workhorse, still useful, mostly superseded.

Evidence: 70
Mechanism: 82
Reliability: 75
Safety: 75
Sourcing: 80
Value: 75
Signal: 65
Staying power: 65

Plain-language summary Intrigue 60 / 100

URB597 is the standard research tool for blocking the FAAH enzyme that breaks down anandamide. Developed by Daniele Piomelli's group at UC Irvine, it permanently inactivates FAAH by latching onto the active site, which raises endogenous anandamide for hours without giving cannabinoids directly. In animal studies it produces anxiolytic and analgesic effects without the cognitive impairment or reward signal that comes with direct CB1 activation, suggesting that elevated endocannabinoid tone might be therapeutically useful. The compound itself never reached human trials, but it laid the conceptual groundwork for clinical FAAH inhibitors like PF-04457845. Not stocked by Kodiac. This monograph is provided for research and educational reference.

Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

Selective FAAH inhibitor (research)

A carbamate inhibitor of fatty acid amide hydrolase (FAAH); the canonical research probe for elevating endogenous anandamide.

Abstract

URB597 (KDS-4103, cyclohexyl carbamic acid 3'-carbamoyl-biphenyl-3-yl ester; CAS 546141-08-6; molecular formula C20H22N2O3; molecular weight 338.40) is a covalent carbamate inhibitor of fatty acid amide hydrolase (FAAH) developed by Piomelli and colleagues at UC Irvine. The compound carbamoylates the active-site serine of FAAH, producing irreversible enzyme inactivation. Selective for FAAH over MAGL and other lipases. Pharmacological consequence: elevation of endogenous anandamide and other N-acylethanolamides without direct CB receptor agonism. The behavioral profile differs from direct CB1 agonists like THC: anxiolytic and analgesic effects without the catalepsy, hypothermia, and intoxication characteristic of CB1 full agonism. Phase 2 clinical trials in major depressive disorder did not demonstrate efficacy; the compound did not advance to phase 3. Plasma half-life is approximately 6 hours; the irreversible mechanism produces effective FAAH inhibition for 24-48 hours after a single dose. Used as the canonical FAAH inhibitor in academic neuroscience.

Mechanism of action

Covalent carbamate inhibitor of FAAH; irreversible carbamoylation of active-site serine. Selective for FAAH over other lipases; elevates endogenous anandamide without direct CB receptor agonism.

Reported research dose ranges

Rodent research 0.1 to 1 mg/kg.

References

Kathuria S, et al. Modulation of anxiety through blockade of anandamide hydrolysis. Nat Med 2003.
Piomelli D, et al. Pharmacological profile of the selective FAAH inhibitor KDS-4103 (URB597). CNS Drug Rev 2006.
Boger DL, et al. Discovery of a potent, selective, and efficacious class of reversible alpha-ketoheterocycle inhibitors of fatty acid amide hydrolase. J Med Chem 2005.

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KDC-MN-328

The full reference document is provided strictly for research use only. It reports research dose ranges from the published literature, not instructions for use in humans or animals.

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FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

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URB597

Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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