UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
 
FORM 6-K

REPORT OF FOREIGN PRIVATE ISSUER PURSUANT TO RULE 13a-16 OR 15d-16 UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the month of September, 2022.
 
Commission File Number: 001-40530

GH Research PLC
(Exact name of registrant as specified in its charter)

28 Baggot Street Lower
Dublin 2
D02 NX43
Ireland
(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F:

Form 20-F
Form 40-F
 ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1): ☐
 
Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7): ☐



On September 22, 2022, at the Interdisciplinary Conference on Psychedelic Research 2022, an investigator will present data related to a Phase 1/2 clinical trial of GH001 (GH001-TRD-102) conducted by GH Research PLC (the “Company”). A copy of the presentation is attached hereto as Exhibit 99.1.

Additionally, on September 23, 2022, an investigator will present data at a poster session related to a Phase 1 clinical trial of GH001 (GH001-HV-101) conducted by the Company. A copy of the poster is attached hereto as Exhibit 99.2.

The fact that these materials are being made available and furnished herewith should not be deemed an admission as to the materiality of any information contained in the materials. The information contained in these materials is being provided as of September 21, 2022 and the Company does not undertake any obligation to update these materials in the future or to update forward-looking statements to reflect subsequent actual results.

1

EXHIBIT INDEX

Exhibit No.
Description
Presentation for September 2022
Poster for September 2022

2

SIGNATURE
 
Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

 
GH Research PLC
Date: September 21, 2022
 
 
By:
/s/ Julie Ryan
 
Name:
Julie Ryan
 
Title:
Vice President, Finance


3

Exhibit 99.1

 A Phase 1/2 Trial of GH001, a Vaporized  5-Methoxy-N,N-Dimethyltryptamine Formulation, inPatients with Treatment-Resistant Depression (TRD)  1  Clinicaltrials.gov ID NCT04698603  GH001-TRD-102  ICPR 2022  Johannes Reckweg1, Cees van Leeuwen1, Cécile Henquet2, Thérèse van Amelsvoort2, Natasha Mason1, Riccardo Paci1, Theis Terwey3, Johannes G Ramaekers1  Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, Netherlands  School Mental Health and Neuroscience, Maastricht University, Maastricht, Netherlands  GH Research, Dublin, Ireland    
 

 Grants  The study was funded by GH Research  Advisory Board/Consultant  Johannes Reckweg and Jan Ramaekers work as consultants for GH Research  2  GH001-TRD-102  ICPR 2022  Disclosures 
 

 ... Remission Rates in TRD < 15%  Established Therapies are Slow-Acting  ~33% no remission   despite 4 treatment steps  Adapted from Trivedi et al., Am J Psychiatry 2006 and Rush et al., Am J Psychiatry 2006  Average time to remission is ~6 weeks  (STAR*D study, Remission Rate Over Time, Treatment Step 1 = Citalopram)  (STAR*D study, Remission Rates Treatment Steps 1 to 4)  3  2 or more prior therapies = TRD  The Problem for Patients with Depression  GH001-TRD-102  ICPR 2022 
 

 5-MeO-DMT (5-Methoxy-N,N-Dimethyltryptamine)  Naturally-occurring psychoactive substance from tryptamine class  Highly potent agonist on 5-HT1A and 5-HT2A receptors  Psychoactive effects with ultra-rapid onset (within seconds) and short duration (5 to 30 min)  GH001 (5-MeO-DMT administration via a proprietary inhalation approach)  Intraday individualized dosing regimen (IDR) for maximization of ultra-rapid remissions   Single visit initial treatment, with no structured psychotherapy   5-MeO-DMT and GH001  4  5-MeO-DMT  GH001-TRD-102  ICPR 2022 
 

 5-MeO-DMT and Peak Experiences  High propensity to induce peak experiences (PE)  Feelings of ego dissolution  Experience of unity or oneness  Profound and meaningful  May be a surrogate marker for therapeutic effects  Assessed through proprietary Peak Experience Scale  Three visual analogue scales (0 – 100):  Intensity  Loss of control  Profoundness  PE defined as total average of ≥ 75  5  GH001-TRD-102  ICPR 2022 
 

 Phase 1 Trial in Healthy Volunteers (GH001-HV-101, n=22)  GH001 single doses of 2 mg, 6 mg, 12 mg, 18 mg and GH001 IDR (6, 12, 18 mg intra-subject dose escalation)  No SAEs, all ADRs mild (except two moderate), all ADRs resolved spontaneously, inhalation well-tolerated  GH001 single dose with psychoactive effect dose response but high inter-subject variability   GH001 IDR controls inter-subject variability achieving a PE1 in all healthy volunteers  6  Clinicaltrials.gov ID NCT04640831; Reckweg et al, 2021  IDR, Individualized Dosing Regimen; SAE, Serious Adverse Event; ADR, Adverse Drug Reaction (an adverse event with a relationship code to the investigational product of definite, probable, or possible, or where code is missing).  PE Scale  PE Threshold  GH001-TRD-102  ICPR 2022 
 

 GH001 Single Dose:  GH001 Individualized Dosing Regimen (IDR): More Chances for Remission  MADRS score  MADRS score  MADRS score  MADRS score  Dose 1  Dose 1  Dose 2  Dose 3  Dose 2  Dose 1  No remission  Remission  Remission  Remission  Remission  Hypothetical   Patient 1  Hypothetical   Patient 2  Hypothetical   Patient 3  Hypothetical   Patient 1  Hypothetical   Patient 2  No remission  No remission  No remission  Dose 1  GH001 – Individualized Dosing Regimen (IDR) Designed to Achieve Ultra-Rapid and Durable Remissions  7  MADRS score  Dose 1  GH001-TRD-102  ICPR 2022  MADRS, Montgomery-Åsberg Depression Rating Scale 
 

 Key Assessments  MADRS 2-hrs  PE Scale  Safety  MADRS 1-day  Cognitive function  Safety  MADRS 7-day  Cognitive function  Safety  GH001  Administration  Day 1  Day 7  Phase 1/2 Trial in TRD (GH001-TRD-102, n=16)  8  PE, Peak Experience; MADRS, Montgomery-Åsberg Depression Rating Scale;IDR, Individualized Dosing Regimen  1Defined as inadequate response to at least two adequate courses of pharmacological therapy or one adequate course of pharmacological therapy and at least one adequate course of evidence-based psychotherapy   Phase 1 (Single Dose)   Phase 2 (IDR)  GH001 12 mg (n=4)  GH001 18 mg (n=4)  TRD1  (n=8)  Primary Endpoint:  Safety until day 7  TRD1  (n=8)  Primary Endpoint:  MADRS remission day 7 (MADRS≤10)  GH001 IDR6, 12, 18 mg to achieve PE  (up to 3 doses, 3h interval)  GH001-TRD-102  ICPR 2022 
 

 Phase 1 (Single Dose) – Efficacy (MADRS)  9  2 of 4 patients in the 12 mg group and 1 of 4 patients in the 18 mg group had a MADRS remission at day 7  2 of 4 patients in the 12 mg group had a PE and both had a MADRS remission at day 7, 0 of 4 patients in the 18 mg group had a PE  PE, Peak Experience; MADRS, Montgomery-Åsberg Depression Rating Scale, MADRS remission, MADRS of ≤10; MADRS response, Reduction of ≥50% from baseline in MADRS; S, Screening; D0-B, Day 0 Baseline; D0-H2, Day 0 2 hours.  MADRS Remission, Response, Improvement Rate at Day 7  MADRS from Screening to Day 7  GH001-TRD-102  ICPR 2022 
 

 Phase 2 (IDR) – Efficacy (MADRS)  10  PE, Peak Experience; MADRS, Montgomery-Åsberg Depression Rating Scale; MADRS remission, MADRS of ≤10; MADRS response, Reduction of ≥50% from baseline in MADRS; S, Screening; D0-B, Day 0 Baseline; D0-H2, Day 0 2 hours.  Primary endpoint met: 7 of 8 patients (87.5%) had a MADRS remission at day 7, p<0.0001  7 of 8 patients had a PE and 6 of those had a MADRS remission at day 7  MADRS Remission, Response, Improvement Rate at Day 7  MADRS from Screening to Day 7  GH001-TRD-102  ICPR 2022 
 

 Phase 1 (Single Dose) and Phase 2 (IDR) – Safety  11  Adverse Drug Reaction, or ADR, an adverse event with a relationship code to the investigational product of definite, probable, or possible, or where code is missingIDR, Individualized Dosing Regimen; C-SSRS, Columbia-Suicide Severity Rating Scale   ADRs  Phase 1 (Single Dose)  Phase 2 (IDR)  ADRs  12 mg (N=4)  18 mg (N=4)  IDR1 (N=8)  MedDRA Preferred Term  n  n  n  Abdominal discomfort        1  Anxiety        2  Depressive symptom        1*  Dizziness  1     Feeling abnormal  1  1     Flashback  1  1  2  Headache  2  1  3  Muscle discomfort  1  Muscle spasms     1     Nausea        2*  Paresthesia        1  Sensory disturbance  3  16-12 mg (N=6); 6-12-18 mg (N=2)  Study Safety Group review  No SAEs  All ADRs mild, except three moderate*  All ADRs resolved spontaneously  Inhalation well-tolerated  No noteworthy changes in vital parameters, except for temporary, non-clinically relevant increase in heart rate and blood pressure shortly after administration of GH001  No clinically significant changes in safety laboratory analyses, psychiatric safety assessments or measures of cognitive function  No safety signal relating to suicidal ideation or suicidal behavior, based on C-SSRS and MADRS subscore item “suicidal thoughts”  GH001-TRD-102  ICPR 2022 
 

 12  GH001 allows rapid and individualized dosing optimization  A single dosing day with GH001 IDR achieved a rapid (within 24 hours) and sustained full remission (7 days) of symptoms of depression in 7/8 patients (87.5%) with TRD  GH001 was well tolerated, and no serious adverse events were reported  Contacts   GH Research: info@ghres.com / clinicaltrials@ghres.com   Maastricht University: johannes.reckweg@maastrichtuniversity.nl / j.ramaekers@maastrichtuniversity.nl  Twitter: @PIMaastricht  Conclusions  GH001-TRD-102  ICPR 2022 




Exhibit 99.2

 INTRODUCTION  5-Methoxy-N,N-Dimethyltryptamine (5-MeO-DMT) is a potent, fast-acting, naturally-occurring psychoactive tryptamine1. It is predominantly found in the bufotoxin of the Sonoran Desert toad2 and was first synthesized in 19363. It acts on the 5-HT1A and 5-HT2A receptors, and it has been suggested that the 5-HT1A subtype is functionally dominant4. 5-MeO-DMT has been used in recreational or self-exploratory contexts2.  5-MeO-DMT has been reported to be proficient in eliciting so called peak psychedelic experiences (PE). These are states during an intense psychedelic experience that are defined by feelings of ego dissolution and experiences of oneness or unity. These can be very profound and meaningful experiences, which may correlate with therapeutic outcomes.  In the current study, 5-MeO-DMT was administered via inhalation as GH001, a novel vaporized 5-MeO-DMT formulation.  AIMS  The primary aim of the study was to investigate safety, tolerability and dose-related psychoactive effects of GH001 in healthy volunteers. Additional aims were to assess the impact of GH001 on cognition, mood, and well-being, as well as to determine the best dosing regimen to reliably elicit a PE.  METHODS  The study was comprised of two single-arm parts, where Part A (n=18) consisted of four single dose levels (2 mg, 6 mg, 12 mg, 18 mg).  Part B (n=4) was comprised of an individualized dosing regimen (IDR), of up to three increasing doses on a single day (6 mg, 12 mg, 18 mg). The part B consecutive doses were only administered if the previous dose did not elicit a PE. This was assessed using a proprietary novel PE scale (PES), consisting of 3 visual analogue scales. Aside from a (medical) screening and the single administration day, follow up visits were conducted on day 1 and day 7 after the dosing day.  A total of 22 healthy volunteers (9 female, 13 male) aged 18 to 42 years (M=29, SD=6.08) with a history of prior psychedelic use participated in the study.  To avoid expectancy effects, participants were not informed about the identity of the study drug until completion of the study.  Measures of the psychedelic experience (PES, EDI, MEQ, CEQ, 5D-ASC) were analyzed using ANOVAs with single factor Dose (5 levels: 2, 6, 12, 18 mg and IDR).   The cognitive tests (DSST, PVT, PMT), measures of well-being (DASS-21, SWLS, FFMQ, CADSS, BPRS), and vital signs were analysed using GLM RM-ANOVAs with the factors Dose (5 levels) and Time (3 levels: Baseline, post-administration, 7-day follow up).  RESULTS  Psychedelic experience  ANOVAs indicated a significant effect of 5-MeO-DMT Dose on ratings of the PES (F4,17 = 9.302, p < .001, ηp2 = 0.686), EDI (F4,17 = 6.925, p = .002, ηp2 = 0.62), MEQ (F4,17 = 8.026, p = .001, ηp2 = 0.654), and Reduction of Vigilance as assessed with the 5D-ASC (F4,17 = 4.023, p = .018, ηp2 = 0.486). The effects of dose on ratings of Oceanic Boundlessness approached significance (F4,17 = 2.901, p = .053, ηp2 = 0.406). Planned contrasts indicated higher mean ratings of the psychedelic experience at higher doses compared to the lowest dose of 2 mg.  A Phase 1, Dose-Ranging Trial to Assess the Safety and Psychoactive Effects of a Vaporized 5-Methoxy-N,N-Dimethyltryptamine Formulation (GH001) in Healthy Volunteers  Reckweg JT1*, Mason NL1, van Leeuwen C1, Toennes SW2, Terwey TH3, Ramaekers JG1 *presenting author  1Department of Neuropsychology & Psychopharmacology, Faculty of Psychology & Neuroscience, Maastricht University, Maastricht, the Netherlands   2Institute of Legal Medicine, University of Frankfurt, Frankfurt, Germany  3GH Research, Dublin, Ireland   Correspondence to:J. G. Ramaekers or J. T. Reckwegj.ramaekers@maastrichtuniversity.nl  johannes.reckweg@maastrichtuniversity.nl  Department of Neuropsychology & PsychopharmacologyT (JGR) +31 43 388 1951  T (JTR) +31 43 388 1530  Maastricht UniversityP.O. Box 6166200 MD Maastricht, the Netherlands  Disclosure statement: The study was funded by GH Research, Dublin, Ireland     Figure 1 Mean (SE) and individual retrospective ratings of the acute psychedelic experience (PES, EDI, MEQ, CEQ) per dose level. Average of ≥75 on PES indicated a PE.  In part A, four participants reported a peak experience (i.e., PES rating ≥75%): one participant at the 6 mg dose, two participants at the 12 mg dose, one participant at the 18 mg dose. In part B, all four participants in the IDR group reached a PE; one participant after first dose (6 mg), two after second dose (6 mg + 12 mg), and one participant after three doses (6 mg + 12 mg + 18 mg).  Cognition and well-being  For the measures on cognition and well-being, no clinically relevant effects of Dose or TimexDose were observed. The factor Time reached significance for the SLWS, BPRS, and the Amnesia and Derealization subscales of the CADSS.  Safety and tolerability  All doses were considered safe and well-tolerated. There were no dropouts and no serious adverse events (AEs) reported. There were two AEs of moderate severity (fatigue, heart rate increase) with all other AEs being mild (e.g. nausea, headache, anxiety), and all AEs resolved spontaneously.  There were no significant effects of Dose on measures of systolic/diastolic blood pressure or heart rate and only a non-clinically significant effect of Time (p=.003), reflecting a mild decrease in heart rate from baseline to 3 hours post-administration (heart rate remained within normal range).   Plasma concentrations  Plasma concentrations of 5-MeO-DMT were very low at 1 hour post-administration and barely measureable at 3 hours post-administration. Bufotenin concentrations were below limit of detection (0.006 ng/ml) at all time points.  Psychopharmacology  in Maastricht  Figure 2 Mean (SE) and individual CADSS and DASS ratings per dose level.  CONCLUSION  Administration of GH001 was well tolerated  Short duration of effects support safety profile  -Individual variability for dose-related effects    IDR may be preferable for clinical applications that aim to optimize therapeutic response  References  1Shulgin, A., and Shulgin, A. (1997). Tryptamines I Have Known and Loved: The Chemistry Continues. Berkeley, CA: Transform Press.  2Weil, A. T., & Davis, W. (1994). Bufo alvarius: A potent hallucinogen of animal origin. Journal of Ethnopharmacology, 41, 1–8.3Hoshino, T., and Shimodaira, K. (1936). Über Die Synthese Des Bufotenin-Methyl-Äthers (5-Methoxy-N-Dimethyl-Tryptamin) Und Bufotenins (Synthesen in Der Indol-Gruppe. Xv). Bull. Chem. Soc. Jpn. 11, 221–224. doi:10.1246/bcsj.11.221  4Krebs-Thomson, K., Ruiz, E. M., Masten, V., Buell, M., and Geyer, M. A. (2006). The Roles of 5-HT1A and 5-HT2 Receptors in the Effects of 5-MeO-DMT on Locomotor Activity and Prepulse Inhibition in Rats. Psychopharmacology (Berl). 189, 319–329. doi:10.1007/s00213-006-0566-1 

 INTRODUCTION  5-Methoxy-N,N-Dimethyltryptamine (5-MeO-DMT) is a potent, fast-acting, naturally-occurring psychoactive tryptamine1. It is predominantly found in the bufotoxin of the Sonoran Desert toad2 and was first synthesized in 19363. It acts on the 5-HT1A and 5-HT2A receptors, and it has been suggested that the 5-HT1A subtype is functionally dominant4. 5-MeO-DMT has been used in recreational or self-exploratory contexts2.  5-MeO-DMT has been reported to be proficient in eliciting so called peak psychedelic experiences (PE). These are states during an intense psychedelic experience that are defined by feelings of ego dissolution and experiences of oneness or unity. These can be very profound and meaningful experiences, which may correlate with therapeutic outcomes.  In the current study, 5-MeO-DMT was administered via inhalation as GH001, a novel vaporized 5-MeO-DMT formulation.  AIMS  The primary aim of the study was to investigate safety, tolerability and dose-related psychoactive effects of GH001 in healthy volunteers. Additional aims were to assess the impact of GH001 on cognition, mood, and well-being, as well as to determine the best dosing regimen to reliably elicit a PE.  METHODS  The study was comprised of two single-arm parts, where Part A (n=18) consisted of four single dose levels (2 mg, 6 mg, 12 mg, 18 mg).  Part B (n=4) was comprised of an individualized dosing regimen (IDR), of up to three increasing doses on a single day (6 mg, 12 mg, 18 mg). The part B consecutive doses were only administered if the previous dose did not elicit a PE. This was assessed using a proprietary novel PE scale (PES), consisting of 3 visual analogue scales. Aside from a (medical) screening and the single administration day, follow up visits were conducted on day 1 and day 7 after the dosing day.  A total of 22 healthy volunteers (9 female, 13 male) aged 18 to 42 years (M=29, SD=6.08) with a history of prior psychedelic use participated in the study.  To avoid expectancy effects, participants were not informed about the identity of the study drug until completion of the study.  Measures of the psychedelic experience (PES, EDI, MEQ, CEQ, 5D-ASC) were analyzed using ANOVAs with single factor Dose (5 levels: 2, 6, 12, 18 mg and IDR).   The cognitive tests (DSST, PVT, PMT), measures of well-being (DASS-21, SWLS, FFMQ, CADSS, BPRS), and vital signs were analysed using GLM RM-ANOVAs with the factors Dose (5 levels) and Time (3 levels: Baseline, post-administration, 7-day follow up).  RESULTS  Psychedelic experience  ANOVAs indicated a significant effect of 5-MeO-DMT Dose on ratings of the PES (F4,17 = 9.302, p < .001, ηp2 = 0.686), EDI (F4,17 = 6.925, p = .002, ηp2 = 0.62), MEQ (F4,17 = 8.026, p = .001, ηp2 = 0.654), and Reduction of Vigilance as assessed with the 5D-ASC (F4,17 = 4.023, p = .018, ηp2 = 0.486). The effects of dose on ratings of Oceanic Boundlessness approached significance (F4,17 = 2.901, p = .053, ηp2 = 0.406). Planned contrasts indicated higher mean ratings of the psychedelic experience at higher doses compared to the lowest dose of 2 mg.  A Phase 1, Dose-Ranging Trial to Assess the Safety and Psychoactive Effects of a Vaporized 5-Methoxy-N,N-Dimethyltryptamine Formulation (GH001) in Healthy Volunteers  Reckweg JT1*, Mason NL1, van Leeuwen C1, Toennes SW2, Terwey TH3, Ramaekers JG1 *presenting author  1Department of Neuropsychology & Psychopharmacology, Faculty of Psychology & Neuroscience, Maastricht University, Maastricht, the Netherlands   2Institute of Legal Medicine, University of Frankfurt, Frankfurt, Germany  3GH Research, Dublin, Ireland   Correspondence to:J. G. Ramaekers or J. T. Reckwegj.ramaekers@maastrichtuniversity.nl  johannes.reckweg@maastrichtuniversity.nl  Department of Neuropsychology & PsychopharmacologyT (JGR) +31 43 388 1951  T (JTR) +31 43 388 1530  Maastricht UniversityP.O. Box 6166200 MD Maastricht, the Netherlands  Disclosure statement: The study was funded by GH Research, Dublin, Ireland     Figure 1 Mean (SE) and individual retrospective ratings of the acute psychedelic experience (PES, EDI, MEQ, CEQ) per dose level. Average of ≥75 on PES indicated a PE.  In part A, four participants reported a peak experience (i.e., PES rating ≥75%): one participant at the 6 mg dose, two participants at the 12 mg dose, one participant at the 18 mg dose. In part B, all four participants in the IDR group reached a PE; one participant after first dose (6 mg), two after second dose (6 mg + 12 mg), and one participant after three doses (6 mg + 12 mg + 18 mg).  Cognition and well-being  For the measures on cognition and well-being, no clinically relevant effects of Dose or TimexDose were observed. The factor Time reached significance for the SLWS, BPRS, and the Amnesia and Derealization subscales of the CADSS.  Safety and tolerability  All doses were considered safe and well-tolerated. There were no dropouts and no serious adverse events (AEs) reported. There were two AEs of moderate severity (fatigue, heart rate increase) with all other AEs being mild (e.g. nausea, headache, anxiety), and all AEs resolved spontaneously.  There were no significant effects of Dose on measures of systolic/diastolic blood pressure or heart rate and only a non-clinically significant effect of Time (p=.003), reflecting a mild decrease in heart rate from baseline to 3 hours post-administration (heart rate remained within normal range).   Plasma concentrations  Plasma concentrations of 5-MeO-DMT were very low at 1 hour post-administration and barely measureable at 3 hours post-administration. Bufotenin concentrations were below limit of detection (0.006 ng/ml) at all time points.  Psychopharmacology  in Maastricht  Figure 2 Mean (SE) and individual CADSS and DASS ratings per dose level.  CONCLUSION  Administration of GH001 was well tolerated  Short duration of effects support safety profile  -Individual variability for dose-related effects    IDR may be preferable for clinical applications that aim to optimize therapeutic response  References  1Shulgin, A., and Shulgin, A. (1997). Tryptamines I Have Known and Loved: The Chemistry Continues. Berkeley, CA: Transform Press.  2Weil, A. T., & Davis, W. (1994). Bufo alvarius: A potent hallucinogen of animal origin. Journal of Ethnopharmacology, 41, 1–8.3Hoshino, T., and Shimodaira, K. (1936). Über Die Synthese Des Bufotenin-Methyl-Äthers (5-Methoxy-N-Dimethyl-Tryptamin) Und Bufotenins (Synthesen in Der Indol-Gruppe. Xv). Bull. Chem. Soc. Jpn. 11, 221–224. doi:10.1246/bcsj.11.221  4Krebs-Thomson, K., Ruiz, E. M., Masten, V., Buell, M., and Geyer, M. A. (2006). The Roles of 5-HT1A and 5-HT2 Receptors in the Effects of 5-MeO-DMT on Locomotor Activity and Prepulse Inhibition in Rats. Psychopharmacology (Berl). 189, 319–329. doi:10.1007/s00213-006-0566-1