To assess healthcare costs and healthcare resource utilization (HCRU) among adult patients who newly initiated erenumab in the United States. This retrospective, non-interventional analysis included adult patients (aged ≥18 years) newly initiating erenumab and who had three consecutive monthly claims for erenumab (11/1/2017-9/1/2019) from the Komodo Health database. Outcomes included migraine-related and all-cause costs, use of other preventive/acute migraine medications, and HCRU. All outcomes were compared during the 180-day pre- versus the 180-day post-index periods. Cost outcomes were also assessed for longer periods including post-index Days 91-270 and monthly mean post-index costs for the longest time of continuous insurance enrollment. Overall, 1839 patients with migraine were included for analysis. Compared to the 180-day pre-index period, an increase in total migraine-related costs (+$2639; p < 0.0001), migraine-related prescription costs (+$3435, p < 0.0001), all-cause total costs (+$2977; p < 0.001), and all-cause prescription costs (+$4102; p < 0.0001) were observed during the 180-day post-index period after adjusting for covariates. Conversely, reduction in migraine-related medical costs (-$896; p < 0.0001), and significantly lower odds of migraine-related emergency room visits (odds ratio [OR] 0.60, 95% confidence interval [CI] 0.44-0.82; p = 0.001), migraine-related office visits (OR 0.58, 95% CI 0.53-0.64; p < 0.0001), and migraine-related neurologist visits (OR 0.69, 95% CI 0.63-0.75; p < 0.0001) were observed during the 180-days post-index period. There were significant decreases in the odds of having overall preventive migraine medications (OR 0.81, 95% CI 0.75-0.87; p < 0.0001), acute-migraine medications (OR 0.92, 95% CI 0.85-1.00; p = 0.038), and triptan (OR 0.79, 95% CI 0.73-0.85; p < 0.0001) during the 180-day post-index period. Sensitivity analyses on cost outcomes found no statistically significant differences in pre-index migraine-related costs compared to post-index migraine-related costs when assessing longer post-index follow-up periods. Initiation of therapy with a novel treatment is often associated with an increase in overall healthcare costs due to the entrance costs associated with novel therapy. For a chronic condition such as migraine, cost versus health benefits should be evaluated over a long period (e.g., ≥2 years) to better understand the true benefits of therapy. Data from this study suggest that the entrance cost for erenumab, the primary driver of the high post-index prescription costs gets mitigated by reduced medical costs over long-term follow-up. The results indicate better disease management in adult patients with migraine, which should be an important consideration for both patients and payors, as these findings have shown an offset between migraine-related prescription and medical costs.