The protective enzyme system (methemoglobin reductase, more properly called cytochrome b5 reductase) is normally present in red blood cells). This reduces the methemoglobin back to hemoglobin, but with high nitrite absorption rates, this protective mechanism is overwhelmed. Interference with the activity of these enzymes can increase the potency of nitrite ingestion.
The symptoms experienced from the ingestion of a toxic dose of sodium nitrite, can include lethargy, confusion, intoxication, nausea and vomiting. In large doses, nitrite acts as a vasodilator because of its relaxing action on vascular smooth muscle, causing a drop in blood pressure (and possible hypotensive headache), A high methemoglobin concentration in the blood gives the skin a brown discolouration.
Note: Some reports have mistakenly attributed a peaceful nitrite death to the vasodilation and drop in blood pressure associated with the production of NO. This has led to the false claim that a lower gastric pH will facilitate [NO] and lead to a more peaceful death.