What nitroglycerin tablets do

Nitroglycerin tablets relax the blood vessels in your heart, allowing more blood and oxygen to reach the heart muscle. When you place a tablet under your tongue, it dissolves quickly and enters your bloodstream within minutes. This relaxation reduces the workload on your heart and eases the chest pain or pressure that comes with angina — a condition where the heart does not get enough oxygen during stress or exertion.

The tablet works fast because the tissue under your tongue absorbs medication directly into blood vessels, bypassing your digestive system. Most people feel relief within 5 to 10 minutes. The effect typically lasts 30 minutes to an hour, depending on the dose and your individual response.

Key Takeaways

  • Nitroglycerin tablets work by relaxing blood vessels so more oxygen-rich blood reaches your heart muscle.
  • You place the tablet under your tongue where it dissolves and enters your bloodstream quickly, usually bringing relief in 5 to 10 minutes.
  • The tablets are used to stop chest pain during an angina attack, not to prevent attacks from happening.
  • If chest pain does not improve after taking one tablet, you should take a second dose after 5 minutes and call emergency services if pain persists after a third dose.
  • Long-acting nitroglycerin forms (patches, ointments, or extended-release pills) work differently and are meant to prevent attacks rather than treat them.

How to use nitroglycerin tablets when chest pain starts

When you feel chest pain or pressure, sit down when ready and place one tablet under your tongue. Do not swallow it — let it dissolve. You can take a second tablet after 5 minutes if the pain has not eased. If pain continues after a third tablet (taken 5 minutes after the second), call 911 or your local emergency number. Do not drive yourself to the hospital.

Keep your tablets in their original brown or amber bottle, which blocks light and keeps them fresh. Store them at room temperature, away from heat and moisture. Nitroglycerin tablets lose strength over time, especially if exposed to air or light, so check the expiration date before you need them. Many people keep one bottle at home and carry a second in their pocket or bag.

Why your doctor prescribes nitroglycerin tablets

Your doctor prescribes nitroglycerin tablets if you have been diagnosed with angina — chest pain caused by reduced blood flow to the heart. Angina often happens during physical activity, emotional stress, or exposure to cold. The tablets give you a way to stop the pain quickly when it occurs, rather than waiting for it to pass on its own.

The tablets are a short-term treatment for an active attack, not a long-term prevention. If you find yourself using nitroglycerin tablets more than once or twice a week, tell your doctor. That pattern suggests your angina is worsening and you may need additional medications or a change in your treatment plan.

Side effects you might notice

Nitroglycerin commonly causes a headache, especially the first few times you use it. This happens because the medication relaxes blood vessels throughout your body, not just in the heart. The headache usually fades as your body adjusts. Taking the tablet with food or water, or lying down for a few minutes, can help.

You may also feel lightheaded, dizzy, or notice your heart beating faster. These effects are temporary and fade as the medication wears off. If you feel faint, sit or lie down until the feeling passes. Rarely, some people develop a rash or feel flushed. Tell your doctor if side effects are severe or do not go away after a few doses.

Medications and substances that interact with nitroglycerin

Never take nitroglycerin if you have used erectile dysfunction medications (sildenafil, tadalafil, vardenafil) in the past 24 to 48 hours. The combination can cause a dangerous drop in blood pressure. Tell your doctor about all medications you take, including over-the-counter drugs and supplements, before starting nitroglycerin.

Alcohol also lowers blood pressure and can increase dizziness or fainting when combined with nitroglycerin. Avoid alcohol, especially around the time you take a dose. If you take blood pressure medications, your doctor may need to adjust the dose once you start nitroglycerin, since both lower blood pressure.

Long-acting nitroglycerin versus short-acting tablets

The tablets you place under your tongue are short-acting — they work quickly to stop pain during an attack. Your doctor may also prescribe long-acting forms: patches you wear on your skin, ointment you rub on your chest, or extended-release pills you swallow. These work differently and are meant to prevent attacks from happening in the first place, not to treat pain once it starts.

Long-acting forms release medication slowly over hours or days, keeping a steady level in your bloodstream. You do not use them when you feel chest pain. If you have both short-acting tablets and a long-acting form, use the tablets only for active pain and use the long-acting form as directed on a regular schedule.

When to seek emergency care

Call 911 when ready if chest pain does not improve after taking three nitroglycerin tablets (one every 5 minutes), if the pain is different from your usual angina, or if you have never had chest pain before. Also call 911 if you feel severe shortness of breath, sweating, nausea, or pain in your arm, jaw, or back along with chest discomfort.

These symptoms can signal a heart attack rather than angina, and a heart attack requires emergency treatment in a hospital. Do not wait or try to drive yourself. Tell the emergency operator that you have chest pain and have already taken nitroglycerin.

Frequently Asked Questions

Can I take nitroglycerin before I expect chest pain?

Some people take a tablet 5 to 10 minutes before an activity they know triggers angina, such as climbing stairs or walking in cold weather. This is called prophylactic use and can prevent pain from starting. Ask your doctor whether this approach makes sense for your situation.

What should I do if I swallow a nitroglycerin tablet by mistake?

Swallowing the tablet means it takes longer to work — 20 to 30 minutes instead of 5 to 10 — because it has to pass through your digestive system. It will still work, but if you need fast relief, place another tablet under your tongue. Call your doctor or poison control if you swallow more than one tablet at once.

Why do I get a headache every time I use nitroglycerin?

Headaches are a common side effect because nitroglycerin widens blood vessels throughout your body. The headache usually lessens after a few doses as your body adjusts. Drinking water, resting, and taking over-the-counter pain relief (such as acetaminophen) can help. If headaches are severe or do not improve, tell your doctor.

How do I know if my nitroglycerin tablets are still good?

Check the expiration date on the bottle. Nitroglycerin loses strength quickly once the bottle is opened, so replace your supply every 3 to 6 months even if the date has not passed. If a tablet does not cause a slight tingling or burning under your tongue, it may have lost strength and should be replaced.

Can I use nitroglycerin if I am pregnant?

Nitroglycerin is generally considered safe during pregnancy when used to treat angina, but you must discuss this with your doctor. Untreated angina poses risks to both you and your baby, so your doctor will weigh the benefits and risks for your specific situation.