Cialis is not a nitrate. It belongs to a completely different drug class called PDE5 inhibitors (phosphodiesterase type 5 inhibitors). However, the reason this question comes up so often is that Cialis and nitrates affect overlapping pathways in the body, and combining them can cause a dangerous, potentially life-threatening drop in blood pressure. The FDA lists nitrate use as a direct contraindication for taking Cialis.
How Cialis and Nitrates Differ
Nitrate medications, such as nitroglycerin, isosorbide dinitrate, and isosorbide mononitrate, are prescribed for chest pain related to heart disease. They work by releasing nitric oxide directly into blood vessel walls. That nitric oxide triggers a chain reaction that relaxes smooth muscle tissue, widening blood vessels and lowering blood pressure. The body breaks down nitroglycerin inside cells to produce nitric oxide as its primary therapeutic effect.
Cialis (tadalafil) works one step further down the same chain. Once nitric oxide has done its job and produced a signaling molecule that relaxes blood vessels, an enzyme called PDE5 normally breaks that molecule down, ending the effect. Cialis blocks that cleanup enzyme, so the relaxation signal lasts longer and is stronger. This is why Cialis improves blood flow to specific areas of the body, but it does not supply nitric oxide the way a nitrate does.
The distinction matters because, while they are chemically unrelated drugs, they amplify each other’s effects on blood pressure in a way that can become dangerous.
Why Combining Them Is Dangerous
Nitrates flood the system with nitric oxide, which produces the signaling molecule that relaxes blood vessels. Cialis prevents that signaling molecule from being broken down. When both are active at the same time, the result is an exaggerated, sustained drop in blood pressure that the body cannot easily correct.
Clinical studies measured exactly how severe this interaction can be. When volunteers took tadalafil and then received nitroglycerin, standing systolic blood pressure dropped below 85 mm Hg in significantly more people compared to those on placebo. Diastolic pressure fell below 45 mm Hg, and some participants experienced systolic drops greater than 30 points. A blood pressure that low can cause dizziness, blurred or fading vision, fainting, nausea, and extreme fatigue. In severe cases, it can lead to shock, with symptoms including cold and clammy skin, rapid shallow breathing, confusion, and a weak pulse.
The FDA’s prescribing label for Cialis states plainly: combining tadalafil with any form of organic nitrate, whether used regularly or occasionally, is contraindicated. The label also warns that this interaction “could cause blood pressure to suddenly drop to an unsafe level, resulting in dizziness, syncope, or even heart attack or stroke.”
The 48-Hour Window
One reason Cialis carries a longer caution period than other erectile dysfunction drugs is its extended duration of action. Tadalafil stays active in the body much longer than similar medications. Clinical data showed that the blood pressure interaction between tadalafil and nitroglycerin lasted up to 24 hours, but was no longer detectable at 48 hours.
Because of this, the FDA label specifies that if someone has taken Cialis and nitrate use becomes medically necessary in a life-threatening emergency, at least 48 hours must pass after the last Cialis dose before a nitrate can even be considered. Even then, the nitrate should only be given under close medical supervision with blood pressure monitoring. This is a wider safety window than for shorter-acting PDE5 inhibitors, and it’s one of the most important practical details for anyone who takes both types of medication at different times.
Common Nitrate Medications to Know About
Nitrates come in many forms, and not all of them are obvious. Prescription nitrates include:
- Nitroglycerin (sold as Nitrostat, Nitro-Dur, Nitromist, Minitran, and others), available as tablets, sublingual tablets, sprays, patches, and pastes
- Isosorbide dinitrate (Isordil)
- Isosorbide mononitrate (Monoket)
Recreational drugs known as “poppers” also contain nitrates or nitrites, typically amyl nitrate, butyl nitrate, or butyl nitrite. These carry the same interaction risk. The MedlinePlus entry for tadalafil specifically warns against combining Cialis with poppers.
If you take any heart or chest pain medication and are unsure whether it contains a nitrate, that’s worth clarifying with a pharmacist before taking Cialis. Some combination medications include a nitrate component that isn’t obvious from the brand name alone.
What Cialis Is Actually Classified As
Tadalafil is one of several PDE5 inhibitors, a class that also includes sildenafil (Viagra) and vardenafil (Levitra). All PDE5 inhibitors share the same nitrate contraindication because they all work through the same mechanism of blocking the enzyme that breaks down the blood vessel relaxation signal. The interaction is not unique to Cialis, though Cialis requires a longer waiting period due to its longer duration in the body.
Cialis is FDA-approved for erectile dysfunction, benign prostatic hyperplasia (enlarged prostate), and pulmonary arterial hypertension (under the brand name Adcirca). In all of these uses, the nitrate contraindication applies equally.