Bomedemstat vs Hydroxyurea for Essential Thrombocythemia (MK-3543-007)

Inclusion Criteria: * Diagnosis of Essential Thrombocythemia (ET) based on World Health Organization Criteria for myeloproliferative neoplasms, and an indication for cytoreductive therapy regardless of age or risk status * Has a centrally assessed bone marrow fibrosis score of Grade 0 or Grade 1, as per a modified version of the European Consensus Criteria for Grading Myelofibrosis * Has received no prior cytoreductive treatment for their ET * Human Immunodeficiency Virus (HIV)-infected participants have well controlled HIV on antiretroviral therapy * Participants who are Hepatitis B surface antigen (HBsAg) positive are eligible if they have received Hepatitis B Virus (HBV) antiviral therapy for at least 4 weeks and have undetectable HBV viral load * Participants with history of Hepatitis C Virus (HCV) infection are eligible if HCV viral load is undetectable Exclusion Criteria: * History of any illness/impairment of gastrointestinal function that might interfere with drug absorption * History of a malignancy, unless potentially curative treatment has been completed with no evidence of malignancy for 2 years * HIV-infected participants with a history of Kaposi's sarcoma and/or Multicentric Castleman's Disease * Has an active infection requiring systemic therapy * Has had a major surgery \<4 weeks prior to first dose of study intervention or has not recovered from side effects of major surgery \>4 weeks prior to first dose