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URB597, also known as KDS-4103, is a potent and selective inhibitor of fatty acid amide hydrolase (FAAH), the enzyme that breaks down the endocannabinoid anandamide. By blocking FAAH, URB597 raises anandamide levels and amplifies endocannabinoid signaling, producing anxiolytic, antidepressant-like, and analgesic effects in animal models without the full intoxicating profile of direct cannabinoid agonists [1][2][3]. It is one of the most extensively used FAAH inhibitor research tools.
- Anxiolytic and antidepressant-like effects in multiple rodent models
- Analgesic activity via enhanced endocannabinoid signaling
- Raises anandamide without the full intoxication profile of direct cannabinoid agonists
- Anxiolytic without a cannabis-type high
- Facilitates fear extinction and trauma recovery
- Antidepressant-like effects via raised anandamide
- Non-opioid analgesia through CB1 and PPAR-alpha
- Irreversibly inhibits an enzyme with broad physiological roles
- Some off-target, CB1- and FAAH-independent effects reported
Overview
URB597 was characterized as a highly potent FAAH inhibitor, blocking the enzyme with nanomolar potency in rat brain membranes and human liver microsomes and showing good selectivity against other cannabinoid-related targets [1]. This clean profile made it the benchmark compound for testing the hypothesis that boosting endogenous anandamide, rather than flooding cannabinoid receptors with an exogenous agonist, could deliver therapeutic effects with fewer side effects.
In behavioral pharmacology, FAAH inhibition with URB597 produced significant effects in standard screens for anxiolytic and antidepressant activity, including the elevated plus maze, tail suspension, and forced swim tests, an effect framework reinforced by studies in FAAH knockout mice [2]. The endocannabinoid system emerged from this work as a genuine target for novel anxiety and mood therapeutics [3]. URB597 has also been shown to influence dopaminergic markers such as tyrosine hydroxylase through mechanisms partly independent of CB1 and FAAH, underscoring that its biology is not limited to simple anandamide accumulation [4].
Despite reaching early clinical evaluation historically, URB597 remains best known as a research standard. It is not an approved medicine and should be treated as an experimental compound, but among the compounds in this batch it has one of the deepest and most reproducible preclinical literatures.
- URB597 raises your own anandamide, sometimes called the bliss molecule, rather than adding an outside cannabinoid.
- It carries the alternate code KDS-4103 from its early clinical development phase.
- URB597 inactivates FAAH by covalently carbamoylating the enzyme's catalytic serine; the crystal structure of the complex revealed a hidden active-site water molecule that normally performs deacylation, which is why the block is effectively irreversible [1].
- Even though it drives brain anandamide well above baseline, URB597 does not cause catalepsy, hypothermia, hyperphagia, or conditioned place preference, and animals do not mistake it for THC; producing THC-like effects requires additionally blocking the 2-AG-degrading enzyme MAGL [2].
- Beyond CB1, URB597 raises the fatty-acid amides PEA and OEA, which activate the nuclear receptor PPAR-alpha; its analgesia in inflammatory pain is blocked by a PPAR-alpha antagonist, revealing a route to pain relief that bypasses cannabinoid receptors [3].
- Over a five-week chronic mild stress protocol, daily URB597 reversed stress-induced anhedonia and body-weight loss about as effectively as the tricyclic antidepressant imipramine [5].
Mechanism
URB597 (also designated KDS-4103) is a potent, systemically active, and highly selective inhibitor of fatty acid amide hydrolase (FAAH), the integral-membrane serine hydrolase that terminates signaling of the endocannabinoid anandamide (N-arachidonoylethanolamine) and of related fatty-acid ethanolamides. Chemically it is an O-aryl carbamate that inactivates FAAH covalently: the enzyme's nucleophilic catalytic serine (Ser241, part of the unusual Ser-Ser-Lys catalytic triad of the amidase-signature family) attacks the carbamate carbonyl, expels the biphenyl leaving group, and forms a stable carbamoyl-enzyme adduct that resists the deacylation step of normal catalysis. A crystal structure of the FAAH-URB597 complex resolved the covalently modified serine and identified a previously uncharacterized active-site water molecule that ordinarily mediates substrate deacylation, clarifying why carbamoylation is effectively irreversible on physiological timescales [1]. Because the inhibition is covalent and only slowly reversible, a single dose yields prolonged suppression of brain FAAH activity.
By blocking hydrolysis, URB597 raises tissue concentrations of anandamide and, to varying degrees, the non-cannabinoid fatty-acid amides palmitoylethanolamide (PEA) and oleoylethanolamide (OEA), all of which are FAAH substrates. Accumulated anandamide acts principally as a partial at CB1 cannabinoid receptors, amplifying tonic, on-demand endocannabinoid tone at synapses already engaged in signaling rather than saturating receptors indiscriminately. PEA and OEA are endogenous ligands of the nuclear receptor PPAR-alpha, and anandamide at higher concentrations can also gate the TRPV1 vanilloid channel; both routes contribute to analgesic and anti-inflammatory actions that are independent of CB1. In a model of inflammatory pain, local URB597 elevated anandamide, 2-arachidonoylglycerol, and PEA, and its antihyperalgesic effect was abolished by a PPAR-alpha , demonstrating a non-cannabinoid-receptor route to pain relief [3].
A defining feature of URB597 is that indirect enhancement of anandamide tone does not reproduce the cannabimimetic tetrad (analgesia, catalepsy, hypothermia, hypomotility) or the abuse-related properties of direct CB1 agonists such as delta-9-tetrahydrocannabinol (THC). The mechanistic basis was clarified by comparison with the dual FAAH and monoacylglycerol lipase (MAGL) inhibitor JZL195: simultaneous elevation of both anandamide and 2-arachidonoylglycerol was required to produce the full tetrad and THC-like drug-discrimination responses, whereas selectively raising anandamide by inhibiting FAAH alone was insufficient [2]. This dissociation explains why selective FAAH inhibition can deliver anxiolytic and antidepressant-like effects while sparing the reward, cognitive, and motor liabilities that limit direct agonists. The benefit is nonetheless dose-dependent; when anandamide is driven very high, recruitment of TRPV1 and additive actions on reward circuitry can shift the response from anxiolytic to anxiogenic and even aversive, as seen when URB597 is combined with exogenous anandamide [4].
Elevated anandamide tone translates into effects across emotion, stress, and pain circuitry. In the chronic mild stress model of depression, five weeks of daily URB597 corrected stress-induced anhedonia and weight changes comparably to the tricyclic imipramine while raising anandamide in midbrain, striatum, and thalamus [5]. Electrophysiological and behavioral studies indicate that URB597 also engages monoaminergic systems, increasing dorsal-raphe serotonergic firing, elevating hippocampal brain-derived neurotrophic factor (), and remodeling and /C receptor sensitivity in a pattern resembling classical antidepressants, with the antidepressant-like response depending on intact synthesis [6]. In fear and trauma paradigms, enhancing anandamide facilitates the consolidation of extinction learning and buffers stress-induced behavioral disruption; these effects are CB1-dependent and have been proposed as an adjunct to exposure-based psychotherapy for post-traumatic stress disorder [7]. Extinction of aversive memory is bidirectionally tuned by the balance of CB1 and TRPV1 signaling that anandamide can access [8], and the direction and magnitude of these endocannabinoid effects can differ by sex and hormonal state [9].
receptor fingerprint
Fatty acid amide hydrolase (FAAH)Potent selective inhibitor (covalent)
Anandamide / CB1 signalingIndirect enhancement
Emotional behaviorAnxiolytic and antidepressant-like modulation
Safetyrisks and cautions, not medical advice
URB597 is a research chemical with no approved human use; although it underwent early clinical study historically, it has no established therapeutic safety profile for general use. In animals it is generally well tolerated and lacks the strong intoxicating and reinforcing effects of direct cannabinoid agonists, but it irreversibly inhibits an enzyme with broad physiological roles, and long-term human consequences are unknown. It should be handled only as an experimental laboratory substance.
History
URB597 was developed in the early 2000s, with much of the foundational pharmacology led by Daniele Piomelli and colleagues, as a tool to validate FAAH as a drug target. Under the designation KDS-4103 it advanced into early clinical evaluation, and it became the reference FAAH inhibitor in hundreds of preclinical studies of anxiety, depression, pain, and addiction, shaping the broader field of endocannabinoid-based therapeutics.
Reputation
URB597 is one of the most recognized and trusted FAAH inhibitor tool compounds in pharmacology, frequently used as the positive control in endocannabinoid research. It has some visibility in nootropic and biohacking discussions because of its anxiolytic and mood effects, but it is not an approved product and is sold only for research. Its scientific reputation is strong; its status as a consumer substance is not.
Subjective profileweighing the evidence above
The best-characterised FAAH inhibitor in the literature and still a laboratory reagent. The anxiolytic and fear-extinction findings are rodent work, and it shuts down a broad enzyme irreversibly, which is not something to do to yourself on a guess. Compelling target, wrong molecule to self-experiment with.
Resources
This entry is here for reference.
Research
- 2006first citedPharmacological profile of the selective FAAH inhibitor KDS-4103 (URB597).
- 2022most recentThe role of the cannabinoid system in fear memory and extinction in male and female mice
- 1.Pharmacological profile of the selective FAAH inhibitor KDS-4103 (URB597).
- 2.Evaluation of fatty acid amide hydrolase inhibition in murine models of emotionality.
- 3.The endocannabinoid system as a target for novel anxiolytic and antidepressant drugs.
- 4.The FAAH inhibitor URB597 efficiently reduces tyrosine hydroxylase expression through CB₁- and FAAH-independent mechanisms.
- 5.Crystal structure of fatty acid amide hydrolase bound to the carbamate inhibitor URB597: discovery of a deacylating water molecule and insight into enzyme inactivation
- 6.Dual blockade of FAAH and MAGL identifies behavioral processes regulated by endocannabinoid crosstalk in vivo.
- 7.Inhibition of fatty acid amide hydrolase and cyclooxygenase-2 increases levels of endocannabinoid related molecules and produces analgesia via peroxisome proliferator-activated receptor-alpha in a model of inflammatory pain.
- 8.The endogenous cannabinoid anandamide has effects on motivation and anxiety that are revealed by fatty acid amide hydrolase (FAAH) inhibition
- 9.Antidepressant-like activity of the fatty acid amide hydrolase inhibitor URB597 in a rat model of chronic mild stress
- 10.The fatty acid amide hydrolase inhibitor URB597 modulates serotonin-dependent emotional behaviour, and serotonin1A and serotonin2A/C activity in the hippocampus
- 11.Enhancing endocannabinoid neurotransmission augments the efficacy of extinction training and ameliorates traumatic stress-induced behavioral alterations in rats
- 12.Effects of endocannabinoid and endovanilloid systems on aversive memory extinction
13 listed here; entry last updated August 2026
Reviews
My notesprivate to this device
FAQ
How is URB597 different from cannabis?
Rather than adding an external cannabinoid, it blocks the enzyme FAAH so your own anandamide accumulates, enhancing endocannabinoid signaling in a more physiological, on-demand way.
Is URB597 approved for anxiety or depression?
No. It is a research compound; although it entered early clinical study as KDS-4103, it is not an approved medicine and is sold only for research.
What is KDS-4103?
KDS-4103 is simply the development code name for the same molecule, URB597.
Limitations of the evidence
- No established human safety profile for general use
Adverse effects
- Irreversibly inhibits an enzyme with broad physiological roles
- Some off-target, CB1- and FAAH-independent effects reported