Inclusion Criteria- Ischaemic Stroke/ Ischaemic lesion on brain imaging in relevant anatomical territory in patients with transient ischaemic attack.
- Age greater than 50 years. -- Consent within one month of stroke.
Exclusion Criteria- Modified Rankin scale score of 5 (at end of the possible enrolment window of one month after stroke).
- Diagnosis of dementia (defined as a documented diagnosis or a screening Informant Questionnaire for Cognitive Decline in the Elderly (IQCODE) score of 3.6 or more).
- Cognitive impairment deemed sufficient to compromise capacity to consent or to comply with the protocol (in the opinion of the local investigator).
- Dependent on daily help from others for basic or instrumental activities of daily living prior to stroke (defined as assistance needed with toileting, walking or dressing).
- Significant co-morbidity or frailty likely to cause death within 24 months or likely to make adherence to study protocol difficult for participant (in the opinion of the local investigator).
- Contra-indication to or indication for administration of allopurinol (as detailed in Summary of Product Characteristics on the XILO-FIST web portal and in trial master file).
- Concurrent azathioprine, 6-mercaptopurine therapy, other cytotoxic therapies, cyclosporin, theophylline and didanosine.
- Significant hepatic impairment (defined as serum bilirubin, Aspartate Aminotransferase (AST) or Alanine transaminase (ALT) greater than three times upper limit of normal (ULN)).
- Estimated Glomerular Filtration Rate < 30 mls/min
- Contraindication to MRI scanning.
- Women who are pregnant or breastfeeding.
- Women of childbearing potential who are unable or unwilling to use contraception.
- Active participation in another Clinical Trial of Investigational Medicinal Product (CTIMP) or device trial or participation within the past month.