Nitroglycerin: what it treats, how to take it, side effects
Last updated September 3, 2026.
Nitroglycerin is a vasodilator - it relaxes blood vessels so the heart needs less oxygen and less work. You may know it as Nitrostat. The under-the-tongue tablet is the rescue for angina attacks - and it comes with a strict 5-minute escalation protocol.
What does it treat?
Episodes of angina - chest pain from coronary artery disease - taken at the first sign of an attack, or 5 to 10 minutes before an activity that usually triggers one.
How do you take it?
Sit down first - it drops blood pressure fast. Place one tablet under your tongue or between cheek and gum and let it dissolve: never chew, crush, or swallow it. Burning or tingling in the mouth is normal but is not proof it is working - do not worry if you feel nothing. The attack protocol your doctor will likely give: one tablet; if the pain has not gone completely after 5 minutes, a second; a third 5 minutes after that; if the pain is not completely gone 5 minutes after the third dose, call 911. Worsening after the first dose can mean calling for help right away - follow your doctor's version exactly. Attacks that become more frequent, longer, or more severe are a doctor call, not more tablets. Use the fewest tablets that relieve the pain - heavy repeated use blunts the effect.
Side effects to know
- Common: flushing - the warmth and redness as the vessels open - and often a headache and lightheadedness from the pressure drop; sitting handles most of it.
- Serious - call your doctor immediately: blurred vision, dry mouth, rash, blistering, or peeling skin, hives, itching, difficulty breathing or swallowing, nausea, vomiting, weakness, sweating, and pale skin - the last set can signal the pressure has fallen too far.
Who should not take it?
Anyone taking the erection or pulmonary-hypertension drugs - tadalafil, sildenafil, vardenafil, riociguat: the combination crashes blood pressure, and this is a hard rule. Right-sided heart attack, severe anemia, and increased pressure in the skull all belong in the prescriber conversation. Store tablets in the original glass container, tightly closed, away from heat and moisture - not the bathroom, not a plastic pillbox - and replace them on schedule: nitroglycerin loses potency.
When is it an emergency?
The protocol itself defines it: chest pain not completely gone 5 minutes after the third tablet is a 911 call - do not drive yourself. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
What a Pymander AI doctor consult looks like
Illustrative example, not a real member's messages.
Common questions
What exactly do I do when chest pain hits?
The standard protocol: stop and sit down - the pressure drop can make you faint standing. One tablet under the tongue or between cheek and gum, let it dissolve, never chew or swallow it. If the pain has not gone completely after 5 minutes, a second tablet; a third 5 minutes later. Pain not completely gone 5 minutes after the third dose: 911. If symptoms worsen after the first dose, your doctor may want emergency help called right then. Get your doctor's exact version at the next visit and keep it with the bottle.
Why does nitroglycerin expire faster than other pills?
The molecule is volatile - it escapes from the tablets into the air, which is why storage rules are strict: original glass container, tightly closed, room temperature, no bathroom humidity, no plastic pillbox. Old tablets lose potency quietly. The practical habit: replace on the schedule the pharmacist gives, carry the glass bottle, and know that a tablet that no longer relieves an attack may be old - but treat non-response as an emergency, not a refill issue.
Why do I feel flushed and headachy after a tablet?
That is the vasodilation itself - blood vessels opening everywhere, not just at the heart. Flushing leads the effects list; headache and lightheadedness are the common companions. They pass in minutes. Sitting for the dose is the safety move. A headache after nitroglycerin is annoying; a headache during chest pain that does not stop is a different story - the 5-minute rule decides.
Why can't I use it with ED medications?
Both relax blood vessels - together they can crash blood pressure dangerously low. MedlinePlus treats nitrates plus tadalafil, sildenafil, vardenafil, or riociguat as a do-not-combine. If both drugs are in your life, your prescribers need to know about each other - and the timing gaps are theirs to specify, not yours to estimate.
Why did my doctor say to use the fewest tablets that work?
Tolerance: nitroglycerin works less well after heavy use - the vessels stop responding. MedlinePlus advises taking the fewest tablets needed to relieve the pain. This is also why attack-pattern changes matter: more frequent, longer, or more severe attacks are a call-your-doctor signal, not a cue to escalate tablets on your own - the disease may be moving.
Can I use it to prevent an attack before exertion?
Yes - that is the second labeled use: one tablet 5 to 10 minutes before an activity that usually triggers angina - stairs, cold weather, intimacy, carrying groceries. Knowing your triggers and dosing ahead of them is good management, not overuse. But if you find yourself pre-dosing for more and more of the day, that pattern change is exactly what your doctor wants to hear about.