Approximately 10.9% of people over 65 live with Alzheimer’s Disease (AD). Individuals with Down Syndrome (DS) are disproportionally affected, with 40-80% developing AD by their 60s. Mouse models and in vitro studies have shown that DYRK1A overexpression is implicated in AD pathology. Reducing DYRK1A expression in AD animal models has shown to improve cognitive function and slow AD onset. Current AD treatments are limited, and DYRK1A inhibitors tested so far show non-specific effects despite promising disease modification. Hence, we aim to reduce the activity of DYRK1A using a novel approach where antisense oligomers (ASOs) are designed to target the DYRK1A transcript. We designed 18 ASOs, resulting in an altered DYRK1A mRNA transcript. The efficiency of these ASOs was assessed using RT-PCR. The three most efficient ASOs were electroporated into DS patient cells and assessed for protein knockdown. This was followed by RNA sequencing and explicit analysis of global changes in both gene expression and splicing patterns to confirm the specificity. At 5μM concentrations, two of our three candidate ASOs achieved significant protein knockdown compared to a positive control. ASO1 and ASO2 showed reductions of 88% ±5% SEM (p = 0.014) and 84% ±5% SEM (p = 0.013), respectively. The analyses on RNA sequencing validated the specificity of the ASO without affecting other genes (p = 3.80×10 ⁻¹⁷). This research introduces a novel therapeutic approach for people at risk of AD including people with DS. We have shown that ASOs can effectively downregulate DYRK1A protein, a potential therapeutic target for AD.