Sodium nitroprusside (SNP), sold under the brand name Nitropress among others, is a medication used to lower blood pressure. This may be done if the blood pressure is very high and resulting in symptoms, in certain types of heart failure, and during surgery to decrease bleeding. It is used by continuous injection into a vein. Onset is nearly immediate and effects last for up to ten minutes.

Common side effects include low blood pressure and cyanide toxicity. Other serious side effects include methemoglobinemia. It is not generally recommended during pregnancy due to concerns of side effects. High doses are not recommended for more than ten minutes. It works by increasing nitric oxide levels in the blood, which increases cGMP levels in cells, and causes dilation of blood vessels.

Sodium nitroprusside was discovered as early as 1850 and found to be useful in medicine in 1928. It is on the World Health Organization's List of Essential Medicines. Sodium nitroprusside is light sensitive, so it needs to be shielded from light to prevent degradation. It is available as a generic medication.

Sodium nitroprusside is intravenously infused in cases of acute hypertensive crises. Its effects are usually seen within a few minutes.

Nitric oxide reduces both total peripheral resistance and venous return, thus decreasing both preload and afterload. So, it can be used in severe congestive heart failure where this combination of effects can act to increase cardiac output. In situations where cardiac output is normal, the effect is to reduce blood pressure. It is sometimes also used to induce hypotension (to reduce bleeding) for surgical procedures (for which it is also FDA, TGA, and MHRA labelled).

The medication is extremely beneficial for use in medical patients because the effects of the medication will directly stop the second that it stops being infused. This is due to the metabolism of the drug, and the rapid inactivation to thiocyanate once conversion of the drug stops.

This compound has also been used as a treatment for aortic valve stenosis, oesophageal varices, myocardial infarction, pulmonary hypertension, respiratory distress syndrome in the newborn, shock, and ergot toxicity.

Sodium nitroprusside should not be used for compensatory hypertension (e.g. due to an arteriovenous stent or coarctation of the aorta). It should not be used in patients with inadequate cerebral circulation or in patients who are near death. It should not be used in patients with vitamin B₁₂ deficiency, anaemia, severe renal disease, or hypovolaemia. Patients with conditions associated with a higher cyanide/thiocyanate ratio (e.g. congenital (Leber's) optic atrophy, tobacco amblyopia) should only be treated with sodium nitroprusside with great caution. Its use in patients with acute congestive heart failure associated with reduced peripheral resistance is also not recommended. Its use in hepatically impaired individuals is also not recommended, as is its use in cases of pre-existing hypothyroidism.