Safety and Efficacy Study Evaluating TRx0237 in Subjects With Mild to Moderate Alzheimer's Disease

Inclusion Criteria: * Diagnosis of all cause dementia and probable Alzheimer's disease * Clinical Dementia Rating (CDR) total score of 1 (mild) to 2 (moderate) and MMSE score of 14-26 (inclusive) * Age \< 90 years * Modified Hachinski ischemic score of ≤ 4 * Females, if of child-bearing potential, must practice true abstinence or be competent to use adequate contraception and agree to maintain this throughout the study * Subject, and/or, in the case of reduced decision-making capacity, legally acceptable representative(s) consistent with national law is/are able to read, understand, and provide written informed consent * Has one (or more) identified adult caregiver who is willing to provide written informed consent for his/her own participation; is able to read, understand, and speak the designated language at the study site; either lives with the subject or sees the subject for ≥2 hours/day ≥3 days/week; agrees to accompany the subject to each study visit; and is able to verify daily compliance with study drug * If currently taking an acetylcholinesterase inhibitor and/or memantine at the time of Screening, the subject must have been taking such medication(s) for ≥3 months. The dosage regimen must have remained stable for ≥6 weeks and it must be planned to remain stable throughout participation in the study. * Able to comply with the study procedures Exclusion Criteria: * Significant central nervous system (CNS) disorder other than Alzheimer's disease * Significant focal or vascular intracranial pathology seen on brain MRI scan * Clinical evidence or history of stroke, transient ischemic attack, significant head injury or other unexplained or recurrent loss of consciousness ≥15 minutes * Epilepsy * Major depressive disorder, schizophrenia, or other psychotic disorders, bipolar disorder, or substance (including alcohol) related disorders * Metal implants in the head (except dental), pacemaker, cochlear implants, or any other non-removable items that are contraindications to MRI * Resides in hospital or moderate to high dependency continuous care facility * History of swallowing difficulties * Pregnant or breastfeeding * Glucose-6-phosphate dehydrogenase deficiency * History of significant hematological abnormality or current acute or chronic clinically significant abnormality * Abnormal serum chemistry laboratory value at Screening deemed to be clinically relevant by the investigator * Clinically significant cardiovascular disease or abnormal assessments * Preexisting or current signs or symptoms of respiratory failure * Concurrent acute or chronic clinically significant immunologic, hepatic, or endocrine disease (not adequately treated) and/or other unstable or major disease other than Alzheimer's disease * Diagnosis of cancer within the past 2 years prior to Baseline (other than basal cell or squamous cell skin cancer or Stage 1 prostate cancer) unless treatment has resulted in complete freedom from disease for at least 2 years * Prior intolerance or hypersensitivity to methylthioninium-containing drug, similar organic dyes, or any of the excipients * Treatment currently or within 3 months before Baseline with any of the following medications: * Tacrine * Clozapine, olanzapine (and there is no intent to initiate therapy during the course of the study) * Carbamazepine, primidone * Drugs with a warning or precaution in the labeling about methemoglobinemia at approved doses * Current or prior participation in a clinical trial as follows: * Clinical trial of a product for cognition within 3 months of Screening (unless confirmed to have been randomized to placebo) * A clinical trial of a drug, biologic, therapeutic device, or medical food in which the last dose/administration was received within 28 days prior to Baseline