CNS effects of histamine H1 antagonists

An accurate evaluation of the functions of the human brain during the administration of drugs is one of the most complex tasks in medical science. In the case of H1 antihistamines, there are many biases that can explain why the interpretation of pharmacological data and those from clinical studies can be very difficult. First of all, the allergic disease itself may modify central nervous system (CNS) functioning and effective medical treatment may accordingly influence the self-reported CNS sensations of patients. Moreover, the carefully selected populations that are enrolled both in pharmacological and clinical studies do not reflect the profile of patients who are treated with such drugs on an everyday basis. Finally, studies of performance impairment and those relying on self-reported sensations may give different and indeed conflicting results. It may be concluded that the various pronouncements on the CNS properties of H1 antihistamines must be treated with some caution.