What happens when you take grapefruit with sildenafil?
Sildenafil (brand names Viagra for erectile dysfunction and Revatio for pulmonary arterial hypertension) is a phosphodiesterase type 5 (PDE5) inhibitor. After an oral dose, it is rapidly absorbed and almost entirely metabolized in the liver and intestine by CYP3A4, with a smaller contribution from CYP2C9. The major metabolite, N-desmethylsildenafil, retains roughly 50 percent of the parent drug's PDE5 activity.
Grapefruit juice contains furanocoumarins, particularly bergamottin and 6,7-dihydroxybergamottin, that inactivate CYP3A4 in the small intestinal wall for 24 to 72 hours. When this gut-wall enzyme is suppressed, more of an oral sildenafil dose escapes first-pass metabolism and reaches the systemic circulation.
In a randomized crossover study of 24 healthy men, two 250 mL glasses of grapefruit juice (one taken an hour before the dose and one given with it) raised sildenafil AUC by about 23 percent and delayed the time to peak concentration (Tmax) by about 15 minutes. Peak concentration (Cmax) was not statistically increased, but interindividual variability was wide.
Why is this important?
A 23 percent average increase is modest compared to flagship grapefruit interactions like buspirone or simvastatin, but it is not nothing. Sildenafil itself is a vasodilator. Its predictable side effects, including headache, facial flushing, nasal congestion, dizziness, indigestion, and a transient drop in blood pressure, are dose-dependent. A modest rise in exposure can push a 50 mg dose into the symptom profile of a 100 mg dose for some users.
The clinical risk is greater for people who are already taking other vasodilators or who have cardiovascular disease. Sildenafil should never be combined with nitrates (nitroglycerin, isosorbide), riociguat, or chronic recreational poppers (amyl nitrite), because the combined drop in blood pressure can be fatal. Adding grapefruit to that combination raises sildenafil even further. Alpha blockers used for benign prostatic hyperplasia (tamsulosin, doxazosin, terazosin, alfuzosin) also lower blood pressure and require careful timing with sildenafil; grapefruit can amplify that drop.
For pulmonary arterial hypertension, Revatio is dosed three times daily at 20 mg, with chronic dosing that meaningfully interacts with chronic CYP3A4 inhibition. Patients on this regimen can experience worsening hypotension and dizziness if they regularly drink grapefruit juice.
What should you do?
For occasional erectile dysfunction use, the simplest approach is to avoid grapefruit and grapefruit juice on the day you plan to take sildenafil. Because the enzyme effect lasts for hours, do not assume that taking the juice in the morning and the medication at night will avoid the interaction.
For chronic dosing (Revatio for pulmonary hypertension, or daily ED dosing), avoid grapefruit, pomelo, and Seville oranges entirely. Sweet oranges, mandarins, clementines, lemons, and limes do not contain meaningful furanocoumarins and are fine.
If you do consume grapefruit and then take sildenafil, monitor for amplified side effects: a more intense headache, more pronounced flushing, lightheadedness on standing, palpitations, or visual disturbances. Sit down and hydrate; if symptoms are severe or you experience chest pain, fainting, or sustained vision changes, seek medical attention.
Never combine sildenafil and nitrates, regardless of grapefruit. If you take nitroglycerin for angina, you should not take sildenafil at all unless cleared by a cardiologist.
Which specific products are affected?
All oral sildenafil formulations are affected, including Viagra tablets, Revatio tablets and oral suspension, and the many generic versions sold worldwide. Injectable Revatio used in inpatient settings bypasses gut metabolism and is not affected by grapefruit.
Other PDE5 inhibitors have similar caveats. Tadalafil (Cialis, Adcirca) is also a CYP3A4 substrate and grapefruit can mildly increase its exposure; because tadalafil has a long half-life (around 17 hours), the practical impact is small. Vardenafil (Levitra) is more strongly affected, as it is heavily dependent on CYP3A4 for clearance and exposure can rise more steeply with grapefruit. Avanafil (Stendra) is the most CYP3A4 sensitive of the four and should not be combined with grapefruit.
The bottom line
Grapefruit juice modestly raises sildenafil blood levels (about 23 percent) through intestinal CYP3A4 inhibition, which can amplify headache, flushing, and lightheadedness. The interaction is manageable for occasional ED use by simply choosing a different juice that day, but should be avoided entirely for chronic Revatio therapy and for anyone also taking nitrates or alpha blockers.