It is well recognized that there is a large variability in drug response. It is estimated that around 50% of patients will not respond to treatment for a wide array of diseases such as migraine and diabetes; this proportion reaches nearly 75% for chemotherapy. This area of research has received much attention recently, culminating in President Barack Obama’s State of the Union address in January 2015 announcing the Precision Medicine Initiative (https://www.nih.gov/precision-medicine-initiative-cohort-program). One of the goals is to “Help develop the right drug for the right person at the right dose,” in stark contrast to the previous focus on developing drugs for a population. The key point in precision medicine is to target drugs to patients that have a high probability of responding well and to limit their use in those patients who will not respond or experience side effects.