First-generation antihistamines are well-known to cause subjective drowsiness. A myriad of studies has also been published that suggest a clear relationship between the use of these drugs and objective performance impairment. Although not all of the tests used in these studies have been validated, the data are fairly consistent, and suggest a difference between earlier (first-generation) sedating antihistamines and the newer (second-generation) nonsedating antihistamines.