Dakota Johnson's effortlessly tousled brunette hair is one of her most defining features, and now we know maintaining those glossy, healthy strands takes more than good genetics. The Madame Web star reportedly keeps her hair in top form with a cult-favorite supplement that's available on Amazon. According to Marie Claire, Johnson takes Nutrafol Women's Balance Hair Growth Supplements to keep her iconic strands long and healthy. You can get undone-yet-glamorous hair with this formula that's designed to promote growth and shine from the inside out.