Single-dose Psychedelic Rapidly and Sustainedly Relieves Chronic Pain and Emotional Disorders: Academic Report on New Original Research in Nature Neuroscience

Background

Chronic pain and emotional disorders (such as anxiety and depression) frequently co-occur in clinical settings, each exacerbating the other and affecting treatment outcomes. Clinical statistics show that patients with chronic pain have a much higher incidence of anxiety or depressive symptoms compared to the general population, while emotional disorders significantly increase the subjective experience of pain, reduce patient compliance with treatment, and raise the risk of opioid abuse. More importantly, the interplay between “pain and emotion” leads to widespread impairment in patients’ quality of life and increased functional disability. Currently, treatment approaches for chronic pain combined with emotional disorders are quite limited; conventional medications and integrated psychological interventions often yield suboptimal results, especially in patients with refractory chronic pain and comorbid depression. The scientific community broadly regards joint assessment and synchronous management of pain and emotional dysfunction as beneficial for patient outcomes, but specific mechanisms and effective interventions remain unclear.

From a neurobiological perspective, chronic pain and anxiety/depressive disorders share overlapping dysfunctions in brain regions. The prefrontal cortex (PFC), anterior cingulate cortex (ACC), amygdala, and insular cortex have all been shown to serve as “bridges” in the development of both pain and emotional disorders. For example, the ACC frequently exhibits hyperactivity in chronic pain animal models and patients, closely tied to abnormal emotional pain perception and attention regulation. The underlying mechanisms involve imbalances in excitation-inhibition, increased glutamatergic neurotransmission, and reduced inhibitory GABAergic function, resulting in heightened neuronal firing. Additionally, enhanced connectivity between the ACC and other pain-related brain regions such as the thalamus and insular cortex intensifies persistent signaling and prolongs disease progression. In depressive disorders, ACC function is complex—sometimes showing excessive activation, sometimes decreased—reflecting not only the emotional symptoms but also the unique neurobiological state of comorbid chronic pain and depression. These findings suggest that the ACC is a critical junction for chronic pain and depressive disorder and thus a potential intervention target.

In recent years, research into psychedelics has entered a new phase. Psilocybin, a naturally occurring indole psychedelic, has long been considered to possess analgesic properties, and is rapidly metabolized in vivo to its active product psilocin. Psilocin mainly targets various serotonin (5-HT) receptors, including 5-HT2A and 5-HT1A, both as partial agonists. Emerging clinical trials and animal studies have shown that psilocybin can rapidly and durably improve symptoms in patients with treatment-resistant depression, anxiety, and chronic pain, but its direct mechanisms and efficacy in chronic pain with comorbid emotional disorders have not yet been systematically studied.

Source and Author Information

This study, titled “single-dose psilocybin rapidly and sustainably relieves allodynia and anxiodepressive-like behaviors in mouse models of chronic pain,” was published in November 2025 in the internationally renowned journal “Nature Neuroscience,” Volume 28, pp. 2285–2295. The corresponding author is Joseph Cichon (joseph.cichon@pennmedicine.upenn.edu), from the Department of Anesthesiology and Critical Care and the Department of Neuroscience, Perelman School of Medicine, University of Pennsylvania, USA. Main authors also include Ahmad Hammo and Stephen Wisser. All experiments were conducted at the John Morgan animal facility at the University of Pennsylvania, with approval from the University’s animal ethics committee.

Detailed Study Design and Workflow

Animal Models and Chronic Pain Induction

Wild-type adult male and female C57BL/6J mice were used in this study, with two classic chronic pain modeling approaches:

1. Neuropathic Pain Model: The “spared nerve injury” (SNI) method, involving left hindlimb exposure of the sciatic nerve, transection of the peroneal and tibial nerves, while sparing the sural nerve.
2. Inflammatory Pain Model: Substantial volume (80-100 µl) of undiluted complete Freund’s adjuvant (CFA) injected into the hind paw, far above conventional doses, to establish a chronic inflammatory pain state. Control animals received an equal volume of saline.
3. Sham and Control Groups: The sham group for SNI only exposed the nerve without manipulation, and the CFA control group was injected with saline.

After modeling, mechanical pain thresholds of the affected limbs were repeatedly measured using an electronic von Frey tester (VF) to monitor behavior and level of injury.

Psychedelic Intervention and Dose Selection

After about four weeks, when mechanical hypersensitivity symptoms had stabilized, psilocybin was administered by single intraperitoneal injection (i.p.). A series of dose-response experiments (0.25, 0.5, 1.0 mg/kg) were conducted to identify the optimal effective dose—0.5 mg/kg was chosen as it elicited the maximal head twitch response (HTR) and substantially reduced activity.

Behavioral and Emotional Disorder Assessment

To comprehensively assess chronic pain with comorbid emotional disorders, multiple behavioral tests were conducted:

• Anxiety Assessment: Elevated plus maze (EPM), open field test (OFT), light/dark box test
• Depression/Despair Assessment: Forced swim test (FST), tail suspension test (TST)
• Motor Skill Evaluation: Rotarod test
• Drug-Induced Preference: Conditioned place preference (CPP)

Tests were performed at multiple time points: pre-modeling (baseline), day 20 post-modeling (chronic phase), after psilocybin intervention on day 28 and day 40, to track behavioral changes.

Local Drug Delivery and Neuronal Activity Visualization

To determine the locus and mechanism of psilocybin’s action, two approaches were used:

1. Intrathecal Injection: Psilocin (the active metabolite) was mixed with rhodamine 6G fluorescent dye and injected into the lumbosacral spinal cord, followed by observation of acute response and cfos activation.
2. Cortical Local Injection: Psilocin was directly injected bilaterally into the ACC, combined with rhodamine 6G for real-time distribution visualization, and two-photon calcium imaging was used in head-fixed, awake mice to record spontaneous calcium activity in Layer ²⁄₃ ACC pyramidal neurons.

Neurotransmitter Receptor Intervention and Mechanism Verification

Selective pharmacological blockade experiments were conducted to probe the molecular mechanism of psilocybin’s effects:

• 5-HT2A Receptor Inverse Agonist: Pimavanserin
• 5-HT1A Receptor Antagonist: WAY-100635

Antagonists were given before psilocybin injection, with systematic observation of pain and emotional behavior changes. Additionally, receptor agonists were used:

• 5-HT2A Receptor Agonist: DOI (2,5-dimethoxy-4-iodoamphetamine)
• 5-HT1A Receptor Agonist: 8-OH-DPAT

These were locally administered individually or in combination to analyze their effects on downstream ACC neuronal activity and behavior.

Data Analysis and Algorithm Application

Behavioral data were analyzed using two-way repeated measures ANOVA, Kruskal-Wallis nonparametric tests, and multiple comparisons correction. Calcium imaging data were quantified using area under the curve (AUC) of neuronal activity. Further, multivariate statistical methods were used to integrate behavioral and electrophysiological results.

Main Findings in Detail

Single-dose Psilocybin Rapidly and Durably Relieves Chronic Mechanical Allodynia

• SNI and CFA model mice exhibited significantly reduced pain thresholds in affected limbs, maintaining stable mechanical allodynia up to day 27, with no significant difference between males and females.
• A single intraperitoneal injection of 0.5 mg/kg psilocybin one day later (day 28) fully reversed mechanical hypersensitivity to baseline levels; the effect persisted for 12 days (end of experiment, day 40), with controls showing no significant improvement.
• This effect was robust across sex, both neuropathic and inflammatory pain models.

Synchronous Relief of Anxiety and Depression-like Behaviors by Psilocybin

• Chronic pain animals (SNI/CFA) exhibited anxiety- and depression-like behaviors in FST, TST, EPM, light/dark box, and OFT—reduced activity, less time in open arms, increased despair time, etc.
• After psilocybin intervention, these metrics significantly improved, showing anti-anxiety and antidepressant effects, with behavioral improvements and pain relief occurring simultaneously and persistently; motor skills also partially recovered.
• Drug preference tests showed that pain animals actively preferred the psilocybin-paired environment rather than control, suggesting that pain and emotional relief have positive motivational attributes.

Local Neuronal Action Sites and Electrophysiological Mechanisms

• Local ACC injection of psilocin markedly reversed mechanical allodynia and some depression-like behaviors in SNI animals, whereas intrathecal injection did not, proving that the effect is primarily cortical rather than spinal.
• Two-photon imaging showed Layer ²⁄₃ ACC pyramidal neurons had heightened spontaneous activity in SNI/CFA mice, and local psilocin application rapidly lowered this excessive activity to normal levels, while the control group showed transient activation.
• Pharmacological effects closely correlated with neuronal electrical activity, indicating that ACC cortical functional state is the biological basis of pain and emotional disorders.

Co-activation of 5-HT2A and 5-HT1A Receptors is Necessary for Psilocybin Action

• Blocking either 5-HT2A or 5-HT1A receptor completely eliminated psilocybin’s reversal of pain and emotional symptoms, with effects persisting to experiment end, indicating that rapid and sustained outcomes require acute receptor-specific activation to initiate long-term mechanisms.
• Use of full agonists (DOI, 8-OH-DPAT), whether individually or combined, only partially attenuated pain or depressive-like behaviors and could not achieve the comprehensive and durable relief seen with psilocybin, signifying the irreplaceable nature of the partial agonist properties of psilocin.

Mechanistic Model and Electrophysiological Molecular Basis

• The study suggests that, in chronic pain (neuropathic and inflammatory) states, ACC pyramidal neurons exhibit upregulated 5-HT2A and downregulated 5-HT1A receptors, leading to sustained over-firing and network dysfunction.
• As a nonselective partial agonist, psilocin can rebalance activity through multiple receptors (especially 5-HT1A and 5-HT2A) within the same cell, suppressing excessive firing and supporting negative emotion modulation and restoration of descending pain control, ultimately remodeling neural circuits to reverse mechanical hypersensitivity and emotional disorders.
• Calcium imaging and pharmacological experiments demonstrated that full agonists (DOI activation, DPAT inhibition), whether alone or in combination, could not fully replicate psilocybin’s “normalization of neuronal electrical activity,” confirming the unique molecular advantage of psilocybin.

Discussion, Significance, and Scientific Value

This study systematically demonstrates for the first time that a single dose of the psychedelic psilocybin can synchronously, rapidly, and durably relieve chronic pain and comorbid anxiety/depression-like behaviors, revealing the core neural circuitry and molecular mechanisms. This advances the theoretical foundation and drug development strategy for integrated treatment of pain and emotional disorders. Key significance includes:

1. Theoretical Innovation: First time proving that chronic pain and emotional disorders are highly integrated in ACC cortical circuits, and that psilocybin achieves acute reversal by unique partial agonism, filling gaps left by typical agonists or antagonists.
2. Application Prospect: Provides a potential new pharmacological intervention for refractory chronic pain with comorbid emotional disturbance (such as cancer pain, fibromyalgia, neuropathic pain, etc.), especially for patient populations exposed to traditional opioids at risk of abuse.
3. Methodological Breakthrough: Innovations such as large-volume CFA modeling, targeted local drug delivery, real-time two-photon ACC imaging offer new research paradigms to neuroscientists.
4. Molecular Mechanism: Reveals the pathogenic role of 5-HT2A/5-HT1A receptor imbalance in pain-emotional disorders, and shows how rebalancing local neuronal activity via the special pharmacology of psilocin provides a foundation for future precision drug development.

Study Highlights

• Both peripheral single-dose psilocybin injection and local ACC psilocin infusion can synchronously reverse chronic pain and emotional disorders, and effects are rapid and persistent.
• ACC cortex rather than spinal cord is the key site of action, the mechanism is suppression of spontaneous high activity in pyramidal neurons.
• Simultaneous partial activation of 5-HT1A and 5-HT2A receptors is essential; full agonism cannot reproduce the “perfect reversal” effect.
• Drug-induced place preference suggests pain relief has positive cognitive and motivational attributes, helpful for understanding improved patient compliance mechanisms.
• Unique CFA modeling turns acute inflammatory pain into a stable chronic model, improving experimental animal translational value.

Other Valuable Information

This study lays a solid foundation for ongoing innovation in precise pharmacological treatment and neural modulation technologies for patients with co-morbid chronic pain and emotional disorders. Future human clinical trials may validate dosage, safety, and efficacy, potentially transforming disease management models.

Furthermore, the research team has publicly shared experimental methods, data, and source code, promoting scholarly exchange and reproducibility, and paving the way for international research collaborations in the cross-disciplinary field of chronic pain and emotional disorders.