A vasodilator is a substance that causes blood vessels in the body to become wider by relaxing the smooth muscle in the vessel wall, or vasodilation. This will reduce blood pressure (since there is more room for the blood) and might allow blood to flow around a clot. Several vasodilators are used as drugs.

Natural vasodilators and drugs that exploit them:

• Adenosine
  • Adenocard - this is primarily used as an anti-arrhythmic.
• Adrenaline and noradrenaline vasodilate arterioles of the skeletal muscles. (By acting on beta-2 adrenergic receptors.) These chemicals cause vasoconstriction elsewhere.
  • Alpha-blockers and Beta-blockers (block the constricting effect of adrenaline).
• Atrial natriuretic peptide (ANP) - a weak vasodilator.
• Bradykinin
• Histamine
  • Complement proteins C3a, C4a and C5a work by triggering histamine release from mast cells and basophil granulocytes.
• Niacin (aka nicotinic acid)
• Nitric oxide
  • Glycerol trinitrate
  • Nitroglycerin
• Platelet activating factor (PAF)
• Prostacyclin (PGI₂) as well as other prostaglandins.
• Tetrahydrocannabinol (THC) - the major active chemical in marijuana. Its mild vasodilating effects redden the eyes of cannabis smokers.