Very dangerous is the combination of poppers with viagra etc.:
from https://en.wikipedia.org/wiki/Poppers:
Studies have proven that the combination of poppers with Viagra can cause a serious decrease in blood pressure and angina attacks during sexual intercourse, which can lead to acute myocardial infarction and sudden death.
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Alkyl nitrites interact with other vasodilators, such as sildenafil (Viagra), vardenafil (Levitra), and tadalafil (Cialis), to cause a serious decrease in blood pressure, which can cause strokes, and low blood pressure leading to people fainting.