Amyl nitrite, nitroglycerin, and sodium nitrite are the forms most used.

They do not act on the skin, but are more or less irritant to mucous membranes. The first two are rapidly absorbed and quickly show physiologic action. Amyl nitrite being very volatile is generally administered by inhalation.

They stimulate the heart, dilate the blood vessels, cause throbbing in the head and flushing of the face. They are rapidly broken up in the system, and their activity is of but short duration. Very large doses can produce death by causing changes in the blood, and vasomotor and respiratory paralysis.

These substances are rapidly changed in the system into nitrates, and are excreted in the urine as such.