Application of a 0.2% nitroglycerin ointment may help heal a long-term (chronic) tear, or fissure, in the anus. You rub a pea-sized dot of cream on the fissure twice a day. It is a good idea to either wear gloves when applying the nitroglycerin cream or wash your hands right after. The skin on your fingers can absorb the medicine and increase your chance of side effects.

An increase in muscle tension, also called resting pressure, in the internal anal sphincter can lead to fissures. Spasms and reduced blood flow to the anus may occur along with the rise in pressure, causing fissures or keeping existing fissures from healing.

Nitroglycerin is usually the first medicine used to treat a chronic anal fissure. Many studies have shown that it works better than conservative treatment (eating more fiber and taking sitz baths).¹

Headaches are the main side effect of nitroglycerin ointment. The risk of headaches and lightheadedness from low blood pressure is especially high if you use too much ointment at one time.

Some people also may experience itching or burning in the anal area. In some cases, people may develop tolerance to nitroglycerin, meaning that after a while the ointment no longer works to reduce muscle tension.

People using nitroglycerin ointment have increased chances of having low blood pressure. So you should not use nitroglycerin ointment within 24 hours of taking sildenafil (Viagra), tadalafil (Cialis), or vardenafil (Levitra).