Importance: In December 2013, the panel members appointed to the Eighth Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC8) published a recommendation that non-Black adults initiate antihypertensive medication with a thiazide-type diuretic, calcium channel blocker, angiotensin-converting enzyme inhibitor (ACEI), or angiotensin receptor blocker (ARB), whereas Black adults initiate treatment with a thiazide-type diuretic or calcium channel blocker. β-Blockers were not recommended as first-line therapy. Objective: To assess changes in antihypertensive medication classes initiated by race/ethnicity from before to after publication of the JNC8 panel member report. Design, Setting, and Participants: This serial cross-sectional analysis assessed a 5% sample of Medicare beneficiaries aged 66 years or older who initiated antihypertensive medication between 2011 and 2018, were Black (n = 3303 [8.0%]), White (n = 34943 [84.5%]), or of other (n = 3094 [7.5%]) race/ethnicity, and did not have compelling indications for specific antihypertensive medication classes. Exposures: Calendar year and period after vs before publication of the JNC8 panel member report. Main Outcomes and Measures: The proportion of beneficiaries initiating ACEIs or ARBs and, separately, β-blockers vs other antihypertensive medication classes. Results: In total, 41340 Medicare beneficiaries (65% women; mean [SD] age, 75.7 [7.6] years) of Black, White, or other races/ethnicities initiated antihypertensive medication and met the inclusion criteria for the present study. In 2011, 25.2% of Black beneficiaries initiating antihypertensive monotherapy did so with an ACEI or ARB compared with 23.7% in 2018 (P =.47 for trend). Among beneficiaries initiating monotherapy, the proportion filling a β-blocker was 20.1% in 2011 and 15.4% in 2018 for White beneficiaries (P <.001 for trend), 14.2% in 2011 and 11.1% in 2018 for Black beneficiaries (P =.08 for trend), and 11.3% in 2011 and 15.0% in 2018 for beneficiaries of other race/ethnicity (P =.40 for trend). After multivariable adjustment and among beneficiaries initiating monotherapy, there was no evidence of a change in the proportion filling an ACEI or ARB before to after publication of the JNC8 panel member report overall (prevalence ratio, 1.00; 95% CI, 0.97-1.03) or in Black vs White beneficiaries (prevalence ratio, 0.96; 95% CI, 0.83-1.12; P =.60 for interaction). Among beneficiaries initiating monotherapy, the proportion filling a β-blocker decreased from before to after publication of the JNC8 panel member report (prevalence ratio, 0.89; 95% CI, 0.84-0.93) with no differences across race/ethnicity groups (P >.10 for interaction). Conclusions and Relevance: A substantial proportion of older US adults who initiate antihypertensive medication do so with non-guideline-recommended classes of medication.