This is a single-center, open-label (participants and researchers are aware about the treatment, participants are receiving), fixed-sequence study in healthy male participants consisting of 2 sequential parts. For all participants enrolled in either part, the study consists of 3 phases: Screening Phase (within 21 to 2 days prior to the first dose administration on Day 1), Open-label Treatment Phase (Day 1 up to Day 12), and Follow-up Phase (7 to 14 days after last dose administration). The maximum duration of study will be 7 weeks per participant. Study will be conducted in 2 parts to understand the relative role of CYP3A4 and amide hydrolysis pathways in JNJ-54861911 metabolism and any potential drug-drug interaction liability with inhibitors of these pathways. Itraconazole will be administered in Part 1 as mixed CYP3A4 and potential amide hydrolysis inhibitor. Clarithromycin will be administered in Part 2 as a pure CYP3A4 inhibitor. However, Part 2 of the study will only be conducted if a relevant interaction is observed with itraconazole based on an interim review of Part 1 data. Participants enrolled in Part 1 will receive single dose of JNJ-54861911, 25 milligram (mg) tablet orally on Day 1 and Day 9 along with itraconazole 200 mg (2*100 mg capsule) orally once daily from Day 5 to Day 12. Participants enrolled in Part 2 will receive single dose of JNJ-54861911, 25 mg tablet orally on Day 1 and Day 9 along with clarithromycin 500 mg immediate release tablet orally twice daily from Day 5 to Day 12. Blood samples will be collected pre-dose (Day 1) up to Day 13 to understand the PK characteristics of JNJ-54861911 and diaminothiazine (DIAT, a metabolite formed after amide hydrolysis of JNJ-54861911). In addition, a blood sample will be collected on Day -1 from all enrolled participants to study genotyping of CYP3A4 gene and other genetic factors that may influence the PK, safety, and/or tolerability of JNJ-54861911 and CYP3A4 inhibitors. Participants' safety will be monitored throughout the study.