In recent, years, researchers have discovered significant differences between men and women in the way they manifest certain illnesses or respond to therapies. Women have different presenting symptoms for a heart attack than men, and certain drugs, including anti-depressants and cancer drugs, may work differently in men and women. In 1994, the National Institutes of Health recommended that most clinical research include an evaluation of gender differences. Nonetheless, females continue to be underrepresented in medical research.