Oxytocin and the Endocannabinoid System: An Unexpected Partnership

For decades, oxytocin and endocannabinoid research occupied separate domains of neuroscience. Oxytocin was studied in the context of bonding, trust, and maternal behaviour. The endocannabinoid system – the brain’s own cannabis-like signalling network – was investigated primarily in relation to pain, appetite, and reward. The discovery that these two systems are mechanistically intertwined, with oxytocin directly driving anandamide production to mediate social reward, ranks among the most important findings in social neuroscience of the past decade.

This page provides a comprehensive, research-backed account of the oxytocin endocannabinoid interaction: how it was discovered, what the molecular pathway looks like, why it matters for understanding social behaviour, and what it means for both oxytocin cannabis research and the development of novel therapies for social deficits. For background on how oxytocin operates as both a hormone and neurotransmitter, see the neuroendocrine page.

The Endocannabinoid System: A Brief Primer

The endocannabinoid system (ECS) is a lipid-based signalling network found throughout the mammalian brain and body. Its key components include:

• Endocannabinoids – the two principal endogenous ligands are anandamide (arachidonoylethanolamide, AEA) and 2-arachidonoylglycerol (2-AG). Both are synthesised on demand from membrane lipids and act as retrograde messengers.
• Cannabinoid receptors – CB1 receptors are densely expressed in the brain, particularly in the cortex, hippocampus, basal ganglia, amygdala, and nucleus accumbens. CB2 receptors are found primarily in immune tissues, though recent evidence shows some brain expression.
• Metabolic enzymes – fatty acid amide hydrolase (FAAH) degrades anandamide, while monoacylglycerol lipase (MAGL) breaks down 2-AG. These enzymes tightly control the spatial and temporal extent of endocannabinoid signalling.

The ECS was discovered through efforts to understand how THC (Δ9-tetrahydrocannabinol) from cannabis produces its effects. Devane et al. (1992, Science) isolated anandamide as the first endogenous cannabinoid – its name derives from the Sanskrit word ananda, meaning bliss. The system was subsequently found to regulate mood, memory, appetite, pain perception, immune function, and – crucially – social behaviour.

Discovery of the Oxytocin-Endocannabinoid Interaction

The first compelling evidence that oxytocin and endocannabinoids cooperate came from Daniele Piomelli’s laboratory at the University of California, Irvine. In a landmark 2015 study published in Proceedings of the National Academy of Sciences, Wei et al. demonstrated that oxytocin drives oxytocin anandamide signalling in the nucleus accumbens to mediate the rewarding effects of social interaction in mice.

The experimental logic was elegant. The researchers first showed that social contact between mice increased anandamide levels in the nucleus accumbens – a brain region central to reward processing. They then demonstrated that this anandamide increase was dependent on oxytocin: blocking oxytocin receptors prevented the social contact-induced rise in anandamide. Conversely, directly infusing oxytocin into the nucleus accumbens was sufficient to increase anandamide production, even without social contact.

The critical test came when the researchers blocked CB1 receptors. Even when oxytocin was present and anandamide was being produced, blocking CB1 receptors abolished the rewarding effects of social interaction. This demonstrated that the pathway runs sequentially: social contact → oxytocin release → anandamide production → CB1 receptor activation → social reward.

Notably, 2-AG – the other major endocannabinoid – was not affected by social interaction or oxytocin, indicating a specific and selective link between the oxytocin receptor and the anandamide branch of the endocannabinoid system (Wei et al., 2015).

The Molecular Pathway: From Oxytocin Receptor to CB1 Activation

Understanding the oxytocin endocannabinoid pathway requires tracing the molecular events from receptor binding to behavioural output.

Step 1: Oxytocin Reaches the Nucleus Accumbens

Oxytocin is released into the nucleus accumbens primarily from parvocellular neurons originating in the paraventricular nucleus (PVN) of the hypothalamus, as well as through somato-dendritic volume transmission (see neuroendocrine dual action). The nucleus accumbens expresses oxytocin receptors, making it a direct target for central oxytocin signalling.

Step 2: Oxytocin Receptor Activation Triggers Anandamide Biosynthesis

The oxytocin receptor (OXTR) is a G-protein coupled receptor (GPCR) that primarily signals through Gαq/11, activating phospholipase C (PLC). The Wei et al. (2015) findings imply that OXTR activation leads to increased activity of N-acyl phosphatidylethanolamine-specific phospholipase D (NAPE-PLD), the enzyme that synthesises anandamide from membrane precursors. The precise intracellular intermediaries remain under investigation, but the functional link – OXTR activation increases anandamide production – is well established.

Step 3: Anandamide Activates CB1 Receptors

The newly synthesised anandamide acts as a retrograde messenger, crossing the synaptic cleft to activate presynaptic CB1 receptors. In the nucleus accumbens, CB1 activation modulates the release of neurotransmitters – including GABA, glutamate, and dopamine – in ways that encode the rewarding value of social interaction. The result is that social contact acquires positive hedonic value: it feels good, and the animal is motivated to seek it again.

Step 4: FAAH Terminates the Signal

Anandamide is rapidly hydrolysed by FAAH, limiting the duration of the signal. This enzymatic degradation provides a natural off-switch and, as we shall see, an important therapeutic target: inhibiting FAAH prolongs and amplifies the anandamide signal, potentially boosting oxytocin-dependent social reward.

Endocannabinoids as Mediators of Oxytocin’s Social Reward Effects

The Wei et al. discovery reframed our understanding of how oxytocin promotes prosocial behaviour. Previous models assumed that oxytocin acted directly on neural circuits to produce its effects. The endocannabinoid intermediary reveals a more nuanced mechanism: oxytocin may function, in part, by co-opting the brain’s own pleasure and reward system through anandamide.

This model received strong support from subsequent work. Don Wei and colleagues demonstrated that FAAH inhibition – which raises anandamide levels by blocking its degradation – enhanced the prosocial effects of oxytocin in mice. Specifically, administering the FAAH inhibitor URB597 alongside low-dose oxytocin produced a synergistic increase in social approach behaviour that neither treatment achieved alone (Wei et al., 2015).

Further evidence came from Daniele Piomelli’s group and collaborators, who showed that the oxytocin anandamide pathway is disrupted in animal models of autism. Mice lacking the oxytocin receptor gene (OXTR knockout mice) failed to show the normal anandamide increase in the nucleus accumbens after social contact, consistent with a severed link between social experience and endocannabinoid reward signalling (Gigliucci et al., 2014, Neuropsychopharmacology – related preliminary work preceding the 2015 paper).

Dolen et al. (2013, Nature) had earlier demonstrated that oxytocin signals in the nucleus accumbens are essential for social reward – specifically, for the phenomenon of social conditioned place preference, where mice prefer environments associated with social interaction. Though this study did not directly examine endocannabinoids, it established the nucleus accumbens as the critical site where oxytocin encodes social reward, setting the stage for Wei’s endocannabinoid findings.

Cannabis, CB1 Desensitisation, and Social Behaviour

The oxytocin cannabis connection is an inescapable implication of this research. If oxytocin’s prosocial effects depend on anandamide signalling through CB1 receptors, then anything that disrupts CB1 receptor function could, in principle, impair social bonding.

Chronic cannabis use is known to downregulate and desensitise CB1 receptors. Hirvonen et al. (2012, Molecular Psychiatry) used PET imaging to demonstrate approximately 20% reductions in CB1 receptor availability across multiple brain regions in daily cannabis users. D’Souza et al. (2016, Biological Psychiatry) confirmed these findings and showed partial recovery after 28 days of abstinence.

If CB1 receptors in the nucleus accumbens are downregulated by chronic cannabis exposure, the oxytocin → anandamide → CB1 → social reward pathway could be attenuated. This provides a neurobiological hypothesis – not yet directly tested in humans – for observations that heavy cannabis use is sometimes associated with social withdrawal, amotivation, and difficulty maintaining close relationships.

Conversely, acute cannabis use activates CB1 receptors and may temporarily enhance some aspects of social experience. Many cannabis users report increased feelings of social connection, empathy, and emotional openness while intoxicated. The oxytocin endocannabinoid framework suggests that these subjective effects may result from exogenous CB1 activation mimicking the downstream effects of oxytocin-driven anandamide release – artificially engaging the social reward pathway without the preceding social interaction or oxytocin signal.

This interpretation aligns with the observation that MDMA (ecstasy) – a drug famous for producing intense feelings of social bonding – dramatically increases plasma oxytocin in humans (Dumont et al., 2009, Journal of Psychopharmacology) and stimulates anandamide release (Nahab et al., 2012). The convergence of oxytocin and endocannabinoid activation may contribute to MDMA’s uniquely prosocial subjective effects.

Cross-Talk Between Oxytocin Receptors and CB1 Receptors

Beyond the sequential signalling pathway described above, emerging evidence suggests more intimate molecular relationships between the oxytocin receptor and CB1 receptor systems.

Bhatt et al. (2017, Progress in Molecular Biology and Translational Science) reviewed evidence for receptor-level interactions, including the possibility that OXTR and CB1R may form heteromeric complexes – physical associations between receptor proteins that alter the signalling properties of each receptor. While direct evidence for OXTR-CB1R heterodimers remains preliminary, heteromerisation between GPCRs is a well-documented phenomenon in the endocannabinoid system: CB1 receptors are known to form functional complexes with dopamine D2 receptors, opioid receptors, and orexin receptors.

Functional cross-talk also occurs at the level of intracellular signalling cascades. Both OXTR and CB1R signal through G proteins that modulate phospholipase C, cyclic AMP, and MAP kinase pathways. The shared use of these intracellular intermediaries creates opportunities for synergy, competition, and mutual modulation at the post-receptor level.

Additionally, oxytocin may influence endocannabinoid tone not only through anandamide biosynthesis but also by modulating FAAH expression. Preliminary data from rodent studies suggest that chronic oxytocin exposure may downregulate FAAH in certain brain regions, effectively prolonging anandamide’s lifespan and amplifying CB1 signalling (Kerr et al., 2013, Neuroscience – reviewed in Mechoulam & Parker, 2013). However, this mechanism requires further confirmation.

Therapeutic Implications

The discovery that oxytocin’s prosocial effects are mediated by anandamide opens novel therapeutic strategies that may circumvent the major pharmacokinetic limitations of oxytocin itself – particularly its poor penetration of the blood-brain barrier.

FAAH Inhibition as a Social Enhancer

If anandamide is the downstream effector of oxytocin’s social reward effects, then raising anandamide levels by inhibiting FAAH could amplify prosocial behaviour without the need to deliver oxytocin to the brain. FAAH inhibitors like PF-04457845 – which has completed Phase II clinical trials for other indications – cross the blood-brain barrier readily and raise brain anandamide levels robustly (Huggins et al., 2012, Pain).

Mayo et al. (2020, Molecular Psychiatry) tested PF-04457845 in a human social anxiety paradigm. FAAH inhibition reduced measures of social anxiety and increased sociability, consistent with augmentation of endocannabinoid-mediated social reward. While this study did not directly measure oxytocin, the results are consistent with the prediction that enhancing anandamide amplifies the same downstream pathway that oxytocin engages.

Autism Spectrum Disorder

Autism is characterised by deficits in social motivation and social reward – functions that appear to depend on the oxytocin-anandamide pathway. Karhson et al. (2018, Molecular Autism) reported that children with autism had lower serum anandamide levels than neurotypical controls, and that lower anandamide correlated with greater social impairment. This suggests a potential biomarker and therapeutic target: if autistic social deficits partly reflect insufficient anandamide signalling, FAAH inhibitors could restore social reward capacity.

This approach may prove more tractable than direct oxytocin administration. As discussed on the neuroendocrine page, intranasal oxytocin has shown inconsistent results in autism trials, possibly because insufficient oxytocin reaches the brain. FAAH inhibitors, by contrast, are small lipophilic molecules that cross the BBB efficiently.

Substance Use Disorders

The social reward pathway is also relevant to addiction, where social isolation and impaired social bonding are both risk factors and consequences of substance use. McGregor and colleagues have proposed that enhancing oxytocin-endocannabinoid signalling could support recovery from addiction by strengthening the rewarding value of social interaction – providing a natural “high” that competes with drug-seeking behaviour (McGregor & Bowen, 2012, Pharmacology, Biochemistry and Behavior).

PTSD and Social Trauma

Post-traumatic stress disorder frequently involves impaired social functioning and difficulty forming close relationships. Both oxytocin and endocannabinoids have independently been implicated in PTSD pathophysiology – low anandamide levels are found in PTSD patients (Neumeister et al., 2013, Molecular Psychiatry), and oxytocin has anxiolytic properties in fear-related paradigms. The convergence of these systems suggests that combination approaches targeting both oxytocin and endocannabinoid pathways may offer synergistic therapeutic benefit.

Future Directions

Several key questions remain unresolved:

• Is the pathway conserved in humans? – The foundational evidence comes from mouse studies. While preliminary human data are consistent (Mayo et al., 2020; Karhson et al., 2018), direct demonstration of oxytocin-driven anandamide release in the human nucleus accumbens has not yet been achieved.
• Does sex modify the pathway? – Oxytocin’s effects are known to be sexually dimorphic, and sex differences in social cognition are well documented. Whether the anandamide intermediary functions identically in males and females is unknown.
• What about 2-AG? – Wei et al. found that oxytocin selectively increased anandamide but not 2-AG. However, 2-AG is the more abundant endocannabinoid and plays critical roles in synaptic plasticity. Whether 2-AG participates in oxytocin signalling under different conditions or in different brain regions remains to be explored.
• Clinical trials – No clinical trial has yet directly tested the hypothesis that FAAH inhibition can treat social deficits by amplifying oxytocin-dependent anandamide signalling. Such trials are a logical next step.

Summary

The discovery that oxytocin endocannabinoid signalling underlies social reward has fundamentally changed our understanding of how the brain motivates social behaviour. Oxytocin does not act alone – it recruits anandamide in the nucleus accumbens, which activates CB1 receptors to encode the rewarding value of social interaction. This pathway explains why social contact feels good, why some drugs (cannabis, MDMA) affect social perception, and why conditions like autism – in which social motivation is impaired – may involve disruptions at multiple points in this circuit.

The therapeutic implications are substantial. Rather than struggling to deliver oxytocin across the blood-brain barrier, clinicians may eventually target the endocannabinoid arm of the pathway – using FAAH inhibitors or other tools to boost anandamide and amplify oxytocin’s downstream effects. This approach is pharmacologically tractable, mechanistically grounded, and supported by growing preclinical and early clinical evidence.

For related topics, see: Oxytocin Structure and Receptor | Oxytocin Neuroendocrine System | Oxytocin Regulation | Oxytocin and Social Behaviour | References

Key References

• Bhatt S et al. (2017) The role of the endocannabinoid system in social behaviour. Progress in Molecular Biology and Translational Science, 148, 61–82.
• Devane WA et al. (1992) Isolation and structure of a brain constituent that binds to the cannabinoid receptor. Science, 258(5090), 1946–1949.
• Dolen G et al. (2013) Social reward requires coordinated activity of nucleus accumbens oxytocin and serotonin. Nature, 501(7466), 179–184.
• D’Souza DC et al. (2016) Rapid changes in CB1 receptor availability in cannabis dependent males after abstinence from cannabis. Biological Psychiatry: Cognitive Neuroscience and Neuroimaging, 1(1), 60–67.
• Dumont GJ et al. (2009) Increased oxytocin concentrations and prosocial feelings in humans after ecstasy (3,4-methylenedioxymethamphetamine) administration. Social Neuroscience, 4(4), 359–366.
• Hirvonen J et al. (2012) Reversible and regionally selective downregulation of brain cannabinoid CB1 receptors in chronic daily cannabis smokers. Molecular Psychiatry, 17(6), 642–649.
• Huggins JP et al. (2012) An efficient randomised, placebo-controlled clinical trial with the irreversible fatty acid amide hydrolase-1 inhibitor PF-04457845. Pain, 153(9), 1837–1846.
• Karhson DS et al. (2018) Plasma anandamide concentrations are lower in children with autism spectrum disorder. Molecular Autism, 9, 18.
• Kerr DM et al. (2013) Alterations in the endocannabinoid system in the rat valproic acid model of autism. Behavioural Brain Research, 249, 124–132.
• Mayo LM et al. (2020) Elevated anandamide, enhanced recall of fear extinction, and attenuated stress responses following inhibition of fatty acid amide hydrolase: a randomized, controlled experimental medicine trial. Biological Psychiatry, 87(6), 538–547.
• McGregor IS & Bowen MT (2012) Breaking the loop: oxytocin as a potential treatment for drug addiction. Hormones and Behavior, 61(3), 331–339.
• Mechoulam R & Parker LA (2013) The endocannabinoid system and the brain. Annual Review of Psychology, 64, 21–47.
• Neumeister A et al. (2013) Elevated brain cannabinoid CB1 receptor availability in post-traumatic stress disorder: a positron emission tomography study. Molecular Psychiatry, 18(9), 1034–1040.
• Wei D et al. (2015) Endocannabinoid signaling mediates oxytocin-driven social reward. Proceedings of the National Academy of Sciences, 112(45), 14084–14089.