Background: Pts treated for CLL with IBR, a once-daily Bruton’s tyrosine kinase inhibitor with dosing flexibility options, may adjust their daily dose to help prevent recurrence or worsening of adverse events, while preserving efficacy. This RW study describes outcomes for CLL pts treated with 1L IBR who did or did not have a DA. Methods: Electronic medical records from the Acentrus database (1/1/2016-4/30/2022) were used to identify CLL pts initiated on 1L IBR (index date). The first 6 months post-index were used to identify pts who remained on a starting dose of 420mg/day or with a DA (reducing to a dose lower than 420mg/day; reasons for DA not available). Treatment adherence (measured by proportion of days covered [PDC] and medication possession ratio [MPR]) and time to next treatment (TTNT) were described for patients with and without a DA. Descriptive analyses are reported for all pts and among a subgroup of pts with high cardiovascular (CV) risk, defined as having a pre-existing CV comorbidity or a high CV risk score (CV subgroup). Results: 1,171 CLL patients were initiated on 1L IBR at the recommended dose of 420mg/day (Table). Of those, 1,038 (88.6%) remained on 420 mg for ≥6 months (mean age=70.2 years, 33.6% female, median follow-up: 30.5 months); 229 (19.6%) had a DA at any time post-index (median time to DA: 5.5 months) and 126 had the DA during the first 6 months (mean age=72.2 years, 42.9% female, median follow-up: 35.1 months). Mean PDC and MPR were descriptively higher in pts with a DA (overall: PDC=0.81, MPR=0.84; CV subgroup: PDC=0.78, MPR=0.81) relative to pts with no DA (overall: PDC=0.70, MPR=0.73; CV subgroup: PDC=0.69, MPR=0.72). Median TTNT was not reached for pts with or without a DA; 12-month Kaplan-Meier (KM) rates were similar for pts with a DA (overall: 89.1%; CV subgroup: 92.7%) and with no DA (overall: 92.5%; CV subgroup: 92.0%). Conclusions: Among CLL pts initiating 1L with standard-of-care IBR, 19.6% had a DA. Those with a DA had descriptively higher treatment adherence with no detriment to TTNT, relative to those who maintained 420mg/day starting dose, regardless of baseline CV risk. These findings are consistent with other RW studies and suggest that IBR DA can be an effective treatment strategy that does not negatively affect efficacy while being well-tolerated outside of clinical trials.