Psilocybin in Functional Neurological Disorder (PsiFUND)

Inclusion Criteria: Age 25 - 60 years. Fluent in the English language A diagnosis of FND from a neurologist and/or neuropsychiatrist as per DSM-5 criteria Moderate or severe symptoms (≥4 on Clinical Global Impression Severity (CGI-S) scale) which have been present for >12 months and have failed to respond to best available treatment. Able to tolerate fMRI scanning procedures. Failed to respond is defined as an inadequate response to a full course of FND-specific therapy, including psychological therapy (cognitive behavioural therapy) or physiotherapy. Either therapy must have been undertaken by a suitably trained expert in FND and must have been specifically targeted at FND symptoms. Exclusion Criteria: Diagnosis of severe depression (defined as meeting DSM-5 criteria) on the MINI 7.0. Positive diagnoses on the MINI will be subject to confirmation at clinical interview by a psychiatrist. Diagnosis of bipolar affective disorder (defined as meeting DSM-5 criteria for bipolar I or bipolar II) on the MINI 7.0. Positive diagnoses on the MINI will be subject to confirmation at clinical interview by a psychiatrist. Diagnosis of a psychotic disorder (defined as meeting DSM-5 criteria) on the MINI 7.0, EXCEPT substance/medication induced psychotic disorder where the duration was limited to the acute period of direct intoxication with the substance/medication. Positive diagnoses on the MINI will be subject to confirmation at clinical interview by a psychiatrist. Diagnosis of drug or alcohol dependence disorder (defined as meeting DSM-5 criteria) on the MINI 7.0. Positive diagnoses on the MINI will be subject to confirmation at clinical interview by a psychiatrist. Diagnosis of a personality disorder (defined as meeting DSM-5 criteria) on the MINI 7.0. Positive diagnoses on the MINI will be subject to confirmation at clinical interview by a psychiatrist. Diagnosis of any dementia (defined as meeting DSM-5 criteria for any dementia disorder) based on clinical interview by a psychiatrist. Diagnosis of any autistic spectrum disorder (defined as meeting DSM-5 criteria for any dementia disorder) based on clinical interview by a psychiatrist. Diagnosis of any learning disability (defined as meeting DSM-5 criteria for any dementia disorder) based on clinical interview by a psychiatrist Significant suicidal behaviour in past 12-months defined using the Columbia-Suicide Severity Rating Scale (C-SSRS) and confirmation based on clinical interview by a psychiatrist Any other factor which would render the participant unsuitable for psilocybin and/or interfere with a supportive therapeutic relationship and/or preclude safe follow-up. Those unable to give informed consent Medical diagnosis incompatible with psilocybin treatment (see Section 8.2.1) Inability to provide a screening blood sample, urine sample or electrocardiogram. Biochemical abnormalities (defined as falling outside the normal reference range) as evaluated by a full blood count, full biochemistry profile and thyroid function tests. Biochemical abnormalities must also be determined as clinically significant by a medical doctor to fulfil the criterion for exclusion. Electrocardiographic abnormalities, defined as any abnormality that is not normal sinus rhythm and determined as clinically significant by a medical doctor. Women of childbearing potential not using contraception. Pregnant or breast-feeding women. Non-registration with a GP or failure to consent to sharing of the GP summary care record and any psychiatric assessments held. Those enrolled in another clinical or research study. Use of any psychedelic substances >2 times in past 12 months. Any factor which would exclude the participant from magnetic resonance imaging (e.g., presence of metal)