Drugs that combat the histamineAntihistamines: Drugs that combat the histaminereleased during an allergic reaction by blocking the action of the histamine on thetissue. Antihistamines do not stop the formation of histamine nor do they stop theconflict between the IgE and antigen. Therefore, antihistamines do not stop the allergicreaction but protect tissues from some of its effects. Antihistamines frequently causemouth dryness and sleepiness. Newer "non sedating" antihistamines are generallythought to be somewhat less effective. Antihistamine side effects that very occasionallyoccur include urine retention in males and fast heart rate.