This article is from the Impotence FAQ, by Sine Nomine firstname.lastname@example.org with numerous contributions by others.
In trials, Viagra caused headaches (16%), flushing (10%), indigestion
(7%), nasal congestion (4%), urinary tract infection (3%), abnormal
vision (3%), diarrhea (3%), and dizziness (1%). Vasomax can cause
stuffy nose and lightheadedness due to low blood pressure. Apomorphine
can cause lightheadedness, fatigue, and nausea. Yohimbine can cause
headaches, sweaty palms, dizziness, and nausea.