This session presents secondary analyses from the 8-week 3-site Multinutrients for ADHD in Youth (MADDY) randomized clinical trial, which randomized 126 children age 6-12 to a 35-ingredient broad-spectrum multinutrient formulation (MN) with all known vitamins and essential minerals vs. placebo. The primary outcome was previously presented: on the blinded clinical global impression, 54% of those taking MN and 18% of those taking placebo responded well (p=0.001). The purpose of this presentation is to understand better how the MN worked, for which children they worked, and how acceptable the dosing of 6-12 capsules./day was. The practical implications of the results included: 1. Parental characteristics (higher education, substance use, anxiety, learning problems) predicted better treatment response. The only child characteristic predicting better treatment response was previous medication. 2. MN influenced immune markers in a favorable direction (anti-inflammatory). 3. Genetic loading did not influence response. 4. The dosing was highly acceptable despite requiring 6-12 capsules.day, but by `1-yr follow-up 46% had discontinued, about the same proportion who did not respond. .