A Study of Ulonivirine (MK-8507) and Methadone in Healthy Volunteers (MK-8507-019)

This study is designed to determine the effect of ulonivirine (MK-8507) on methadone in the body. Participants will take methadone alone and then methadone with ulonivirine to see if ulonivirine changes how the body processes methadone.

Inclusion Criteria The main Inclusion Criteria include but are not limited to: * Is in good health * Has a body mass index (BMI) between \>18 and ≤40 kg/m\^2 * Is reliably participating in a methadone maintenance program for at least 2 months prior to Day 1 and is on a documented stable dose of methadone for at least 14 days prior to Day 1 Exclusion Criteria The main Exclusion Criteria include but are not limited to: * Has a history of cancer (malignancy) * Has a history of significant multiple and/or severe allergies, or has had an anaphylactic reaction or significant intolerability to prescription or nonprescription drugs or food * Has tested positive human immunodeficiency virus (HIV) or for a sexually transmitted infection at screening * Is under the age of legal consent