PsilOCD: A Pharmacological-Challenge Feasibility Study

Key Inclusion Criteria:

* Aged 20 to 65 years;
* Any gender;
* A primary diagnosis of OCD (based on the Mini-International Neuropsychiatric Interview (M.I.N.I.));
* Has met diagnostic criteria for OCD for at least 12 months;
* Willing to comply with protocol and associated lifestyle restrictions;
* Adequate understanding of the English language to give informed consent and participate in the study;
* Participant can attend visits as an outpatient;
* Comfortable using a computer, access to internet from home, and willing to participate in some of the study visits via video-link.

Key Exclusion Criteria:

* Current or past history of dependent (according to ICD10 criteria) substance use (not including nicotine and/or caffeine), Tourette's syndrome, autism spectrum disorder, epilepsy, organic mental disorder, or a personality disorder apart from obsessive-compulsive personality disorder;
* Current or past history of psychosis or mania in themselves or a first-degree relative;
* Unstable physical health;
* Significantly abnormal clinical test result;
* Heavy smoker, or unable to attend the dosing days (including the subsequent recovery part) without a smoking break;
* Unwillingness to allow their GP or mental health practitioners to be informed of their participation (or, to allow study team access to Summary Care Record).