Short answer: In the label's fixed-dose trials, the most common Viagra side effects were headache (16% to 28% vs 7% on placebo), flushing (10% to 19% vs 2%), indigestion (3% to 17% vs 2%), abnormal vision such as a color tinge (up to 11% on 100 mg vs 1%) and nasal congestion. Several rose with dose. Viagra has no boxed warning; using it with nitrates is contraindicated.
What Viagra is approved for: Viagra is a PDE5 inhibitor approved to treat erectile dysfunction (ED) (section 1). It is not indicated for use in women or children (sections 8.1, 8.4). Sildenafil is also sold as Revatio for pulmonary arterial hypertension, and the two are not taken together (section 5.7).
Source
VIAGRA (sildenafil citrate) tablets, for oral use, prescribing information and Patient Information. Viatris Specialty. DailyMed, version published February 13, 2026. DailyMed setid d905dc8d-917f-4ea3-a4ee-a1ecf6967d4e
No. The current Viagra label has no boxed warning.
These are the label's own numbers from the Adverse Reactions section. Where the label compares with placebo (a dummy treatment), both columns are shown, so you can see how much more often a reaction happened on Viagra.
| Adverse reaction | 25 mg (n=312) | 50 mg (n=511) | 100 mg (n=506) | Placebo (n=607) |
|---|---|---|---|---|
| Headache | 16% | 21% | 28% | 7% |
| Flushing | 10% | 19% | 18% | 2% |
| Dyspepsia | 3% | 9% | 17% | 2% |
| Abnormal Vision | 1% | 2% | 11% | 1% |
| Nasal Congestion | 4% | 4% | 9% | 2% |
| Back Pain | 3% | 4% | 4% | 2% |
| Myalgia | 2% | 2% | 4% | 1% |
| Nausea | 2% | 3% | 3% | 1% |
| Dizziness | 3% | 4% | 3% | 2% |
| Rash | 1% | 2% | 3% | 1% |
Abnormal vision was mild to moderate and transient, mostly a color tinge to vision, but also more sensitivity to light or blurred vision. Stopping because of side effects in placebo-controlled studies: 2.5% on Viagra vs 2.3% on placebo.
| Adverse reaction | VIAGRA N=734 | PLACEBO N=725 |
|---|---|---|
| Headache | 16% | 4% |
| Flushing | 10% | 1% |
| Dyspepsia | 7% | 2% |
| Nasal Congestion | 4% | 2% |
| Abnormal Vision | 3% | 0% |
| Back Pain | 2% | 2% |
| Dizziness | 2% | 1% |
| Rash | 2% | 1% |
Placebo-controlled trials of 2 to 26 weeks in which people took Viagra as needed, at least once a week, which matches the recommended way to take it. Only one person stopped because of abnormal vision.
Viagra was given to over 3,700 men aged 19 to 87 before approval, and over 550 were treated for more than a year. At doses above the recommended range, side effects were similar but more frequent.
In healthy volunteers, Viagra lowered lying-down blood pressure by a mean maximum of 8.4/5.5 mmHg. With amlodipine in people with high blood pressure, Viagra 100 mg added a mean drop of 8 mmHg systolic and 7 mmHg diastolic (section 5.5).
Two observational studies suggested about a 2-fold higher risk of NAION (a sudden optic nerve problem) right after PDE5 inhibitor use, with risk estimates of 2.15 (95% CI 1.06, 4.34) and 2.27 (95% CI 0.99, 5.20). The label says this does not establish cause.
Reported after approval: heart attack, sudden cardiac death, irregular heartbeat, stroke and bleeding in the brain, mostly in men with existing heart risk factors and often during or shortly after sex; seizures, transient global amnesia, nosebleeds, eye problems, sudden hearing loss, prolonged erection and blood in the urine.
In healthy volunteers given single doses up to 800 mg, side effects were similar to lower doses but more frequent and more severe.
The Warnings and Precautions part of the label lists these. Each line gives the label's heading and what it means in plain words.
Do not use with nitrates or riociguat. Viagra must not be used with nitric oxide donors such as organic nitrates or nitrites in any form, taken regularly or now and then, or with guanylate cyclase stimulators such as riociguat, because blood pressure can drop sharply. The label says it is unknown when a nitrate can be given safely after Viagra. It is also contraindicated after a known allergy to sildenafil (Viagra or Revatio).
Heart risk with sexual activity. Viagra is generally not used by men for whom sex is inadvisable because of their heart. Caution is used with aortic stenosis or poor blood pressure control, and there are no controlled data after a heart attack, stroke or life-threatening arrhythmia in the last 6 months, with resting blood pressure under 90/50 or over 170/110, or with heart failure or unstable angina.
Prolonged erection. Erections lasting more than 4 hours and priapism (painful erections over 6 hours) have been reported infrequently. An erection lasting more than 4 hours needs immediate medical help, as untreated priapism can permanently damage the penis. Caution is used with a deformed penis or conditions such as sickle cell anemia, multiple myeloma or leukemia.
Sudden vision loss. Sudden loss of vision in one or both eyes may be a sign of NAION. The label says to stop all PDE5 inhibitors, including Viagra, and seek medical attention. People who have had NAION are at higher risk of it again, and there are no controlled data in retinitis pigmentosa.
Sudden hearing loss. Sudden decrease or loss of hearing, sometimes with ringing in the ears and dizziness, has been reported. The label says to stop Viagra and seek prompt medical attention.
Alpha-blockers and blood pressure medicines. Viagra can add to the blood-pressure-lowering effect of alpha-blockers and other blood pressure medicines, which can cause dizziness or fainting. With an alpha-blocker, the person is stable on it first and Viagra starts at the lowest dose.
Ritonavir. Ritonavir raises sildenafil levels about 11-fold, so the label lowers the Viagra dose. Low blood pressure, fainting and prolonged erection were seen in some volunteers given high doses (200 to 800 mg).
Other PDE5 inhibitors and ED treatments. Viagra with Revatio, other sildenafil products or other ED treatments has not been studied and is not recommended, as blood pressure may drop further.
Bleeding. Bleeding events have been reported, without an established cause. Safety is unknown in people with bleeding disorders or active stomach ulcers.
Sexually transmitted diseases. Viagra offers no protection against sexually transmitted diseases, including HIV.
From the Patient Information that comes with Viagra:
Dose Track has a side-effect log. Each entry records the symptom, a severity (none, mild, moderate, severe or life-threatening), the date and an optional note, and can be tied to a specific dose or logged on its own. The history screen shows what you logged over time, which makes it easier to tell your prescriber when a reaction started and whether it is easing. The app records what you enter; it does not judge whether a symptom is serious. For anything on the label's call-your-doctor list, call your doctor.
This page is what the FDA label says, in plain words. It is not medical advice. Follow your prescriber, and ask them or your pharmacist about anything here.