Health information influences consumer decision making to seek, select, and utilize services. Online searching for mental health information is increasingly common, especially by adolescents and parents. We examined historical trends and factors that may influence population-level patterns in information seeking for attention-deficit/hyperactivity disorder (ADHD). We extracted Google Trends data from January 2004 to February 2020. Keywords included "ADHD," "ADHD treatment," "ADHD medication," and "ADHD therapy." We examined trends (systematic change over time) and seasonality (repeating pattern of change) via time-series analyses and graphics. We also used interrupted time-series analyses to examine the impact of celebrity and pharmaceutical events. Queries of "ADHD medication" increase, while queries for "ADHD therapy" remain relatively low despite a positive linear trend. Searches for "ADHD treatment" displayed a downward trend in more recent years. Analyses on seasonality revealed that holiday breaks coincided with a decrease in search interest, while post-break periods illustrated a rise, and the ADHD Awareness Month (October) coincided with a rise of public interest in all four search terms. Celebrity effects were more prominent in earlier years; the "Own It" pharmaceutical campaign may have increased ADHD awareness and the specificity of searches for "ADHD medication." The anonymous, accessible, and low-cost nature of seeking information online makes search engines like Google important sources of mental health information. Changing search patterns in response to seasonal, advocacy, and media events highlight internet-based opportunities for raising awareness and disseminating empirically supported information.