Antihypertensive therapy is associated with significant relative risk reductions in the incidence of heart failure, myocardial infarction, and stroke. However, a common adverse reaction to antihypertensive therapy is orthostatic hypotension, dehydration, and syncope. We propose that continued use of antihypertensive medications at the same dosage during the dry summer months in patients living in the Sonoran desert leads to an increase in syncopal episodes.

All hypertensive patients who were treated with medications and admitted with International Classification of Diseases, 9th Revision code diagnosis of syncope were included. They were defined as “cases” if they presented during the summer months (May to September 2012) and “controls” if they presented during the winter months (November 2012 to March 2013). The primary outcome measure was the presence of clinical dehydration. The statistical significance was determined using the 2-sided Fisher exact test.

A total of 496 patients with an International Classification of Diseases, 9th Revision code diagnosis of syncope were screened, and 179 patients were included in the final analysis. In patients taking antihypertensive medications, there were a significantly higher number of cases of syncope secondary to dehydration or orthostatic hypotension during the summer months (45%) compared with the winter months (26%) (P = .01). The incidence of syncope was significantly higher in older patients (63%) compared with younger individuals (37%) during the summer months.

The incidence of syncope increases during the summer months among people who reside in a dry desert climate and who are taking antihypertensive medications. On the basis of our findings, we describe an easily preventable condition that we define as the “Summer Syncope Syndrome.” We recommend judicious reduction of antihypertensive therapy in patients residing in a hot and dry climate, particularly during the summer months.