Psilocybin in Patients With Fibromyalgia: EEG-measured Brain Biomarkers of Action

Inclusion Criteria: * Fibromyalgia lasting for more than 3 months, as diagnosed by an appropriate medical professional using the American College of Rheumatology diagnostic criteria. * Over 18 years of age * United Kingdom (UK) resident registered with a primary care medical practice * Sufficiently competent in English with capacity to provide written informed consent * Agreement for research team to contact primary and/or secondary care team over the course of the study * No psychedelic use in the past 6 months Exclusion Criteria: * Current or previously diagnosed psychotic disorder or bipolar disorder * Immediate family member with a diagnosed psychotic disorder * History of serious suicide attempts or presence of significant suicide/self-harm risk at screening * Emotionally unstable personality, history of mania, or other psychiatric problem that the screening clinician feels may jeopardise the therapeutic alliance and/or safe exposure to psilocybin * Currently using medication which could interact with psilocybin including anti-psychotics, mood stabilizers \& serotonergic antidepressants including selective serotonin reuptake inhibitors (SSRIs), SNRIs, and tricyclic antidepressants (TCAs)\* * On waiting list for interventional treatment for pain (e.g. surgery or targeted injections) * Actively enrolled on pain management programme over course of study or awaiting further investigations for pain * Contraindications to EEG components of the study (e.g., epilepsy, migraine, focal scalp sensitivity) * MRI contraindications (e.g. claustrophobia, metal implants) * Physical co-morbidities that are unsuitable for the psychedelic component of the study (e.g., epilepsy, severe cardiovascular disease, insulin-dependent diabetes, hepatic or renal failure e.g., CrCl \< 30ml/min etc) * Blood or needle phobia * Positive pregnancy test at screening or during the study * People who are breastfeeding * Unable to engage with physical demands of dosing session (i.e. attend centre and remain in research facility for an extended period of time) * Unable to access virtual meetings/phone for remote follow-ups * Patients consuming more than 35 units of alcohol per week. * Presence of new or un-investigated 'red flag' symptom indicating need for urgent investigation (e.g. upper motor neuron syndrome, gait ataxia, bladder or bowel dysfunction). * Limited life expectancy (\<18 months) or rapidly deteriorating condition that may inhibit completion of the study (6 month remote foll…