A Study to Assess Safety, Tolerability, and Efficacy of HTL0018318 in Patients With Dementia With Lewy Bodies

Inclusion Criteria: * Diagnosed with probable DLB according to the fourth revision of consensus diagnostic criteria for DLB. * Clinical imaging evidence from either SPECT or MIBG cardiac scintigraphy that is consistent with a clinical diagnosis of DLB. * Partner or caregiver able to support the patient for the duration of the clinical trial. Exclusion Criteria: * Patients with a diagnosis of Parkinson disease at least 1 year prior to onset of dementia. * Patients with the presence of severe extrapyramidal symptoms * Patients with the presence of an illness/condition apart from DLB that could contribute to cognitive dysfunction * Patients with poorly controlled hypertension despite lifestyle modifications and/or pharmacotherapy, who are currently on more than 2 different antihypertensive treatments * Patients with prominent, recurrent episodes of syncope are related to orthostatic hypotension * Patients with pulmonary disease or evidence of clinically significant moderate or severe pulmonary symptoms * Patients who are taking a range of prohibited and restricted medication * Patients who have been prescribed individualised cognitive rehabilitation, stimulation or training that was performed under medical supervision in the 6 months prior to the screening visit * Patients who have any known condition(s) that may be contraindicated or interfere with the completion of the nuclear imaging scans.