The 'vasovagal effect' of nitrates: an under-recognised complication of nitrate use.

Nitrates are useful drugs in cardiovascular medicine. They have a presumed vasovagal effect, which is a rare but often under-recognised complication that is partly caused by central inhibition of the sympathetic nervous system. However, no consistent variable associated with the presumed vasovagal effects following nitrate administration can be identified, and there are only limited reports of the phenomenon in the literature. In fact, the true prevalence of such a complication is unknown, because no data from observational studies exist, although it would seem likely to be a rare event. A greater awareness and recognition of this unusual effect of nitrate use is necessary in view of the increasing use of nitrates. Fortunately, recovery is generally the rule with supportive management.