PDE5 Inhibitor & Nitrate Interaction Calculator
Emergency Warning
If you've already taken both medications, seek emergency medical care immediately. Do not wait. Call 911 or go to the nearest ER. Tell them you took a PDE5 inhibitor and a nitrate.
When you take a PDE5 inhibitor like Viagra or Cialis for erectile dysfunction, and you also take nitroglycerin for chest pain, something dangerous can happen - your blood pressure can crash. Not just a little drop. A profound hypotension that can lead to fainting, heart attack, or even death. This isn’t a rare theoretical risk. It’s a well-documented, life-threatening interaction that’s been known since the late 1990s. And yet, many people still don’t know about it.
How the Interaction Works
Both PDE5 inhibitors and nitrates work through the same chemical pathway in your body - the nitric oxide (NO) and cyclic GMP (cGMP) system. This system controls how blood vessels relax. When blood vessels relax, your blood pressure drops. That’s good if you’re trying to improve blood flow to the penis. It’s dangerous if your whole body’s blood vessels open up too much. Nitrates - like nitroglycerin, isosorbide dinitrate, or isosorbide mononitrate - break down into nitric oxide. Nitric oxide then tells your blood vessels to relax by boosting cGMP levels. PDE5 inhibitors - including sildenafil (Viagra), tadalafil (Cialis), vardenafil (Levitra), and avanafil (Stendra) - block the enzyme that breaks down cGMP. So when you take both, you’re not just increasing cGMP production; you’re also stopping it from being cleared. The result? cGMP builds up to unsafe levels, your blood vessels stay wide open, and your blood pressure plummets. Studies show how extreme this can get. In one trial published in Circulation, 46% of men who took sildenafil and nitroglycerin together had their systolic blood pressure drop below 85 mm Hg when standing. For comparison, only 24% of those on placebo did. Even lying down, 36% of the combination group hit that dangerous low, compared to just 6% in the placebo group. This isn’t a mild side effect. It’s a medical emergency.How Long the Risk Lasts
Not all PDE5 inhibitors are the same. Their half-lives - how long they stay active in your body - determine how long you need to wait before taking nitrates.- Sildenafil (Viagra) and vardenafil (Levitra) last about 4 hours. You need at least 24 hours between doses.
- Avanafil (Stendra) has a similar half-life of 5-6 hours. Same 24-hour rule applies.
- Tadalafil (Cialis) sticks around much longer - about 17.5 hours. That means you must wait 48 hours before using any nitrate.
It’s Not Just Prescription Nitrates
Many people think only medical nitrates are dangerous. But recreational drugs called “poppers” - amyl nitrite or butyl nitrite - are also nitric oxide donors. They’re sometimes used for sexual enhancement, especially in gay communities. Combining poppers with PDE5 inhibitors has led to multiple case reports of sudden, severe hypotension. One patient in the Journal of Sexual Medicine went into shock after using both. He survived, but barely. Even some dental anesthetics or inhaled nitrous oxide (laughing gas) aren’t risky - they don’t raise nitric oxide levels enough to trigger the cascade. But if you’re unsure, assume it’s dangerous. When in doubt, wait.
What to Do If It Happens
If you or someone else takes both and starts feeling dizzy, nauseous, sweaty, or like they’re about to pass out - act fast.- Have the person lie down with their feet elevated (Trendelenburg position). This helps blood flow back to the heart and brain.
- Call emergency services immediately. Say: “I took a PDE5 inhibitor and a nitrate.” That tells responders exactly what’s happening.
- Do not give more medication. Don’t try to “shake it off.”
- IV fluids are the standard treatment in the ER. They help restore blood volume and pressure.
The Controversy: Is the Risk Overblown?
Here’s where things get messy. In 2022, a study of over 3,000 patients in a U.S. health database found no significant increase in heart attacks or fainting among people who had both prescriptions. Only 27% of them even got a warning from their doctor. Many seemed to manage it safely by spacing out doses. Some experts argue the absolute ban might be too strict. Dr. Donald S. Nuzum, a pharmacist who reviewed the data, says, “The real-world risk appears lower than the theory suggests.” He points out that patients who know about the interaction often avoid taking nitrates on days they use PDE5 inhibitors. But here’s the counterargument: the consequences of getting it wrong are catastrophic. One death is one too many. The American Heart Association, European Society of Cardiology, and the FDA still say: never combine them. Even if most people are careful, one mistake can be fatal.
Who’s at Risk - And Who Isn’t
About 52% of men over 40 have erectile dysfunction. Nearly 18 million Americans have coronary artery disease. That means a lot of people are on one or both of these drugs. About 8-12% of men prescribed PDE5 inhibitors also get nitrates. But not everyone needs nitrates. Many men with angina can switch to safer alternatives like beta-blockers or calcium channel blockers. In fact, the Princeton IV guidelines suggest doctors should ask: “Do you really need nitrates?” If the chest pain only happens during sex, the real solution might be better heart control - not more nitrates. Patients who’ve been on nitrates for years often know how to manage their condition. They might skip their morning dose on days they plan to use Viagra. That’s smart. But they still need to be told - and told clearly.How to Stay Safe
If you’re on a PDE5 inhibitor:- Ask your doctor if you’re taking any nitrate - even patches or sprays.
- Know the exact waiting time: 24 hours for Viagra, Levitra, Stendra; 48 hours for Cialis.
- Carry a wallet card (like the one from the Princeton Consensus) that lists your meds and the warning.
- Never take poppers with any PDE5 inhibitor.
- If you’re unsure about a new medication, check with your pharmacist. Say: “I take Cialis. Is this safe?”
- Screen every patient for nitrate use before prescribing a PDE5 inhibitor.
- Document it in the chart. Don’t assume they know.
- Give them written instructions. Verbal warnings alone aren’t enough.
- Use electronic alerts in your system. Only 37% of U.S. clinics have them.
The Future: Will This Rule Change?
A new PDE5 inhibitor is in phase II trials (NCT04876321) designed to avoid this interaction. It’s not yet approved, but if it works, it could change everything. The American Heart Association plans to update its guidelines in 2024. They’re reviewing real-world data. Maybe, someday, the rule won’t be “never,” but “only if you wait 48 hours and are monitored.” But for now? The safest choice is simple: don’t mix them. Ever. If you need both, talk to your doctor about alternatives. Your life isn’t worth the risk.Can I take Cialis and nitroglycerin if I wait 24 hours?
No. Cialis (tadalafil) has a half-life of about 17.5 hours, meaning it stays active in your body for nearly two full days. The FDA and major medical guidelines require a minimum 48-hour gap between Cialis and any nitrate. Waiting only 24 hours is not enough and could still lead to dangerous hypotension.
Are all erectile dysfunction drugs equally risky with nitrates?
Yes, all PDE5 inhibitors - including Viagra, Cialis, Levitra, and Stendra - interact with nitrates in the same way by blocking cGMP breakdown. The difference is in how long they last. Sildenafil and vardenafil need 24 hours between doses; tadalafil needs 48 hours. Avanafil also requires 24 hours. None are safe to combine with nitrates without strict timing.
Do over-the-counter supplements like L-arginine interact with PDE5 inhibitors?
No. L-arginine is an amino acid that the body uses to make nitric oxide, but it doesn’t raise blood levels high enough to trigger the dangerous interaction. Dietary nitrates from vegetables like spinach or beets also pose no risk. The danger comes only from pharmaceutical-grade nitrates or recreational nitrites like poppers.
What if I accidentally took both? Should I go to the ER?
Yes. Even if you feel fine, the drop in blood pressure can happen suddenly and without warning. Symptoms like dizziness, nausea, blurred vision, or cold, clammy skin mean you need emergency care. Don’t wait. Call 911 or go to the nearest ER. Tell them you took a PDE5 inhibitor and a nitrate.
Can I use nitroglycerin if I took Viagra yesterday?
If you took sildenafil (Viagra) 24 hours ago and have no other PDE5 inhibitor in your system, it’s generally considered safe to use nitroglycerin. But only if you’re certain you didn’t take another dose within the past 24 hours. If you’re unsure, or if you take other medications, consult your doctor before using nitrates.
