When something restricts blood flow to the heart muscle, a person may experience intense chest pain that doctors call angina. People can use the drug nitroglycerin to relieve this pain.

Most often, the reason for this decrease in blood flow is plaque formation and the narrowing of the arteries supplying blood to the heart.

Nitroglycerin helps open up the blood vessels and allows blood to flow. People can also use nitroglycerin to treat anal fissures.

This article provides an overview of nitroglycerin, including its uses, how it works, possible side effects, interactions, and warnings.

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Nitroglycerin is a medication that treats angina and anal fissures. It works by promoting blood flow.

The body breaks nitroglycerin down into nitric oxide. Nitric oxide causes the smooth muscle within the blood vessels to relax. This allows the arteries and veins to open up, allowing more blood to flow through. Healthcare professionals call this action vasodilation.

During an angina attack, a person will experience intense chest pain. Nitroglycerin will start working within 1–3 minutes, but its maximal effect occurs after 5 minutes.

Different forms of the medication start working at different time periods, depending on their formulation. For example:

  • sublingual tablet: 1–3 minutes
  • translingual spray: 1–3 minutes
  • extended-release tablet: 60 minutes
  • topical ointment: 15–30 minutes
  • transdermal patch: 30 minutes
  • intravenous: immediately

The medication’s maximal effect also depends on its formation. For example:

  • sublingual tablet: 7 minutes
  • translingual spray: 4–15 minutes
  • extended-release tablet: 2.5 to 4 hours
  • topical ointment: 60 minutes
  • transdermal patch: 120 minutes
  • intravenous: immediately

When people use nitroglycerin for anal fissures, the ointment will relax the anal sphincter, which is the muscle tissue around the anus, and lower pressure in the anus. This promotes blood flow to the area and helps the fissure heal.

Doctors usually use nitroglycerin to treat the pain associated with angina.

The narrowing of the arteries that supply the heart with blood is what causes unstable angina. Doctors call this condition coronary artery disease (CAD).

CAD is the most common type of heart disease. Almost 366,000 people in the United States die every year because of CAD.

Nitroglycerin allows the blood vessels to open up, letting oxygen and nutrient-rich blood feed the heart muscle. This action offers immediate relief from chest pain.

People can also use nitroglycerin to treat anal fissures. Anal fissures are tears in the skin of the anus. People can develop anal fissures from passing hard stools.

Similar to its effects on angina, nitroglycerin as a rectal ointment helps the healing process by stimulating blood flow to the affected area.

The following table lists the different formulations of nitroglycerin.

Form of nitroglycerinHow to use
aerosol solution
dissolve under the tongue
24-hour patch
apply to the skin
rectal ointmentrectal use only


When someone is experiencing intense chest pain, it is vital to resolve this symptom as quickly as possible. People can also take fast-acting nitroglycerin formulations 5–10 minutes before doing an activity that may cause an angina attack.

The aerosol spray, pumpspray, packet, and tablet are all fast-acting forms of nitroglycerin. The following sections look at these forms in more detail.

Aerosol spray and pumpspray

People can use these devices by giving one or two sprays on or under the tongue once they feel angina pain. They should not inhale the spray.


A sublingual packet of nitroglycerin contains 400 micrograms of nitroglycerin powder. A person places the contents of the packet under their tongue when angina pains begin.


At the first sign of angina pain, a person should place the tablet under their tongue or between the gums and the cheek. The tablet will dissolve and absorb through the tissues of the mouth.

People who use the aerosol spray, pumpspray, packet, or tablet should not swallow the drug. Nitroglycerin will absorb through the mouth tissues on its own. This provides faster relief than swallowing the medication. People should also avoid rinsing or spitting for 5 minutes after administering the dose.

A person can take each of these forms of fast-acting nitroglycerin at 5-minute intervals. If they do not feel relief from the intense chest pain, they can take two more doses 5 minutes apart.

If someone has taken three doses of a fast-acting formulation and does not experience any pain relief, they need medical attention immediately.

There are also two other formulations of nitroglycerin that can prevent angina attacks. These are not fast-acting, so people should not use them to stop an attack when it is happening.


Nitroglycerin patches come in doses ranging from 0.1 milligrams per hour (mg/hr) to 0.8 mg/hr.

A person places the patch on their skin anywhere except the areas below the knee and elbow. Most people place the patch on their chest. The area should be clean, dry, and hairless to allow the nitroglycerin to absorb across the skin.

A person should leave the patch on their skin for 12–14 hours and remove it for 10–12 hours. People usually have the patch on during the day and remove it during sleep.


People can apply nitroglycerin ointment to their skin using a dose-measuring applicator that comes with the tube. A person measures the desired dose onto the measuring applicator and then places the applicator ointment side down on the skin.

They then spread the ointment across the skin. The person should not rub the medication in but allow the ointment to absorb across the skin. Finally, they tape the applicator to the skin.

People apply two doses of ointment each day. Doctors usually tell people to use the ointment first thing in the morning and reapply it 6 hours later.

Anal fissures

The rectal ointment for anal fissures contains 0.4% nitroglycerin. A person inserts the ointment into their anus every 12 hours for up to 4 weeks. If symptoms persist, a person may take the medication for another 4 weeks, totaling 8 weeks.

To apply the rectal ointment, a person covers their finger with plastic wrap and puts 1 inch of ointment along the finger. They then insert the finger into the anal canal up to the first finger joint. The person then smears the ointment around the area.

If this is too painful, the person may apply the ointment to the outside of the anus instead.

People may experience many side effects when using nitroglycerin, including:

When people use nitroglycerin for relieving angina, they should be in a relaxed, seated position.

A person’s blood pressure can drop significantly after using nitroglycerin. If they stand up too quickly after administering the dose, their blood pressure may drop even lower and put them at risk of fainting.

The most common side effect of long-acting nitroglycerin is a headache, but this side effect decreases with medication use.

Although people only apply rectal ointment to the anus, they may still experience headaches and dizziness.

Some people may have allergies to nitroglycerin, so doctors do not recommend that people use it if they have a history of allergic reactions to this medication.

Doctors do not prescribe nitroglycerin to anyone with a history of severe anemia, heart attack occurring on the right side of the heart, or increased pressure in the brain.


Nitroglycerin contraindications include allergic reactions, though these reactions are rare. Other contraindications include:

Nitroglycerin may interact with certain other medications, such as PDE-5 inhibitors.

PDE-5 inhibitors are drugs that doctors give to treat erectile dysfunction. Viagra, Cialis, and Levitra are PDE-5 inhibitors. As with nitroglycerin, these drugs also cause increased blood flow and can lower blood pressure.

Doctors do not recommend that people use nitroglycerin with PDE-5 inhibitors, as these medications can cause fainting if someone is taking them together.

People should avoid using nitroglycerin if they have taken Viagra or Levitra within the past 24 hours or Cialis within the past 48 hours.

Anyone using long-acting nitroglycerin cannot take PDE-5 inhibitors.

The nitroglycerin dosage may be different for different people. For example, the dosage may depend on the form of the drug a person is using. It can also change based on:

  • the condition a person is using the medication to treat
  • the person’s age
  • the severity of the condition
  • other medical conditions the person has
  • how the person reacts to the first dose

Generic nitroglycerin comes in the form of a sublingual tablet. The strengths of these tablets are 0.3 mg, 0.4 mg, and 0.6 mg.

Brand-name nitroglycerin, Nitrostat, comes in the form of a sublingual tablet. The strengths of this tablet are 0.3 mg, 0.4 mg, and 0.6 mg.

An overdose of nitroglycerin may occur when a person uses PDE-5 inhibitors with nitroglycerin or uses too much nitroglycerin during an angina attack.

Severe side effects that doctors associate with a nitroglycerin overdose include:

  • a sudden drop in blood pressure
  • an increased heart rate
  • increased blood flow and pressure in the brain
  • throbbing headaches
  • confusion
  • dizziness
  • disturbances in vision

Currently, no drug can reverse a nitroglycerin overdose. That said, doctors can provide care to people experiencing an overdose by giving them intravenous fluids and elevating their legs.

Using nitroglycerin in the appropriate way can delay the serious complications of angina, which include heart attack, stroke, and even death.

People may experience side effects with nitroglycerin, so they should remain seated while the drug takes effect.

Nitroglycerin can interact with erectile dysfunction medications. People with angina should report the use of Viagra, Cialis, and Levitra to a doctor because using both drugs together may be dangerous.

People can also treat anal fissures using nitroglycerin rectal ointment. Side effects and interactions can also occur with the topical use of nitroglycerin.