5.1. There is some slight, but ambiguous, evidence from epidemiological studies of a connection between antihistamine use and traffic collision rates. Of note, these epidemiological studies were done primarily when the use of 1st -generation (but not 2nd -generation) antihistamines was prevalent.

5.2 There is overwhelming evidence from the experimental literature that the 1st -generation antihistamines produce objective signs of skills performance impairment as well as subjective symptoms of sedation.

5.3 The 2nd -generation antihistamines show low incidence of objective skills performance impairment and in the majority of cases no evidence of subjective sedation.

5.4 While 2nd -generation antihistamines represent a major triumph for the pharmaceutical industry in reducing potential side effects, there still remains some evidence that all antihistamines, even the 2nd - generation drugs, can have objective skills impairment consequences at least in some cases.

5.5 Within both the 1st - and 2nd -generation antihistamine groupings, there is considerable variation in objective evidence of impairment. Additionally, for the 1st -generation antihistamines, there is considerable variation in subjective effects, such as sedation. Within each generation of antihistamines, there clearly are drugs that are to be preferred for use to avoid side effects.

5.6. It would appear that proper selection of a 2nd -generation antihistamine would produce little skills performance impairment and only a small effect on traffic collisions.

5.7. Methodologically, it is apparent that among the many diverse techniques for investigating driving-related impairment, some methods and behavioral domains are more sensitive to the effects of antihistamines. Obviously, reports of the rate of impairment can be manipulated by a failure to use sensitive measures or test at appropriate post-dose times. In future studies of antihistamines, therefore, it would be hoped that more utilization will be made of the most methodologically-sound techniques so as to permit a better comparison between different drugs.

Note: please refer back to the Table of Contents for links to the Figures and Appendices.