Ibrutinib, a once-daily Bruton tyrosine kinase inhibitor, is a standard-of-care first-line (1L) treatment for patients with chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL). Dosing flexibility (adjustment to daily dose of <420 mg/d) with ibrutinib can help prevent recurrence or worsening of adverse events while maintaining long-term efficacy. This study compared time to next treatment among patients with CLL/SLL in the United States initiating 1L single-agent ibrutinib at 420 mg/d (index date) and staying on this dose vs patients with dose adjustment (DA) within 3 to 12 months. Two databases were used: Komodo claims (a majority from community practices) and Acentrus electronic medical records (from academic and nonteaching hospital systems). To account for immortal time bias (patients with DA survived on 1L therapy until DA) and overlap between follow-up time and definition of treatment strategies, a target trial emulation approach was used, in which patients were cloned at index date and contributed follow-up to both treatment strategy arms until deviation from the strategy. Among 3343 patients in Komodo (mean age: 67.5 years; 37.6% female) and 1171 patients in Acentrus (mean age: 70.4 years; 34.6% female) who initiated 1L single-agent ibrutinib 420 mg/d, 18.0% and 19.6%, respectively, had a DA. DA was not associated with an increased risk of having a next treatment in both databases (adjusted hazard ratio [95% confidence interval]: Komodo: 0.95 [0.80-1.14], Acentrus: 1.14 [0.80-1.62]). These findings suggest that a flexible dosing approach with ibrutinib may be effective in allowing patients to achieve optimal outcomes while remaining on long-term continuous 1L treatment.