A method for determining the appropriate dosage of a medication to treat Attention Deficit Hyperactivity Disorder (ADHD) in an individual who has ADHD. The method comprises sampling the peripheral skin temperature of left and right like extremities of an individual during a predetermined time interval when the individual is in a sensory deprived state to provide respective left and right sampled peripheral skin temperature data; processing the sampled peripheral skin temperature data; processing the sampled peripheral skin temperature data including filtering, differentiation, and conversion to the frequency domain to derive spectral signatures whose magnitudes are indicative of the level of ADHD manifestation. The effectiveness of the medication is calculated by comparison to predetermined threshold values.