A Study of MP-101 in Dementia-Related Psychosis and/or Agitation and Aggression

Inclusion Criteria: * Females must be of non-childbearing potential, defined as women greater than or equal to (≥) 60 years of age, postmenopausal women ≥50 and less than (\<) 60 years of age who have had a cessation of menses for at least 12 months, or women who are congenitally or surgically sterile * Males must agree to use 2 forms of highly effective birth control with female partners of childbearing potential while enrolled in the study, and for at least 28 days following the last dose * Ambulatory (with or without walking device) with a stable gait * Have a Mini-Mental State Examination (MMSE) score of 10 to 24 * Meet clinical criteria for one of the following disorders: dementia associated with Parkinson's disease, dementia with Lewy bodies, possible or probable Alzheimer's disease, frontotemporal degeneration spectrum disorders, vascular dementia * Able to communicate verbally * Have an NPI score of ≥4 on either individual item (delusions or hallucinations) or ≥6 on the Psychosis Subscale (combined delusions and hallucinations), or an NPI score of ≥4 on agitation/aggression domain * Have a reliable caregiver who provides written informed consent to participate and who is in frequent contact with the patient (defined as spending at least 4 hours/day at least 4 days/week with the patient and who is knowledgeable about the patient's daytime and nighttime behaviors). The caregiver must be able to communicate with site personnel, and opinion of the investigator, must understand the written protocol-specified questionnaires. If a caregiver cannot continue, one replacement caregiver will be allowed if the above criterion is met * Must be on a stable dose of cholinesterase inhibitor and/or memantine, if applicable * If taking antipsychotic drugs or any drug intended to treat psychosis, must be on a stable treatment regimen for ≥1 month prior to the study * Have venous access sufficient to allow for blood sampling per the protocol * Have clinical laboratory test results within normal reference range for the population or investigative site * Are capable of participating in all study assessments * Are able and willing to provide consent (patients and caregivers) Exclusion Criteria: * Have a history of significant psychotic disorders (including, schizophrenia, delusional disorder, substance abuse psychosis that lasted over 6 months, major depressive disorder or bipolar disorder with psychotic episodes) * Has a history of ischemic stroke within the last 12 months or any evidence of hemorrhagic stroke * Have renal impairment as defined by Estimated Glomerular Filtration Rate (eGFR) \<45 milliliters per minute per 1.73 square meters (ml/min/1.73m2) * Have significant cardiovascular, respiratory, gastrointestinal, renal, hematologic, or oncologic comorbidities that could impact patient safety and study participation over 10 weeks * Have a history of seizures or other condition that would place the patient at increased risk of seizures. * Are, in the investigator's judgment, at risk for suicide, or as indicated by the Columbia Suicide Severity Rating Scale (C-SSRS) * Have a Fridericia's corrected QT interval (QTcF) greater than (\>) 450 milliseconds (ms) for males or 470 ms for females * Are currently enrolled in any other clinical trial involving an investigational product or any other type of medical research judged not to be scientifically or medically compatible with this study * Have participated, within the last 30 days, in a clinical trial involving an investigational product. If the previous investigational product has a long half-life, at least 3 months (or more) must have passed * In the opinion of the investigator or sponsor, are unsuitable for inclusion in the study