Take note: pupil size can tell the true story of attraction, even when people are unaware of their own attraction to another person. Check out this Dartmouth College study using functional magnetic resonance imaging of the amygdala. But watch out! Antihistamines and tricyclic antidepressants may cause mydriasis (enlarged pupils). This can cause confusion and mixes signals. In other words, the person may not really be attracted to you at all, he or she may just be on drugs.