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Key facts at a glance
- Most common
- Headache: 16%, 21% and 28% at 25, 50 and 100 mg vs 7% on placeboViagra (sildenafil) label · DailyMed
- Urgent warning
- Erection lasting more than 4 hours: get medical help right awayViagra (sildenafil) label · Patient Information
- Drug clearance, not symptom duration
- Sildenafil and its active metabolite have terminal half-lives of about 4 hoursViagra (sildenafil) label · Clinical Pharmacology
- Compounded status
- The Mendoxa compounded tablet is not FDA-approvedFDA compounding Q&A
Viagra side effects by dose: the FDA label table
Headache was the most common reaction at every studied dose. The Viagra (sildenafil) label reports the exact rates below; some reactions increased with dose, but not every row rises at every step.
| Side effect | Viagra 25 mg (n=312) | Viagra 50 mg (n=511) | Viagra 100 mg (n=506) | Placebo (n=607) |
|---|---|---|---|---|
| Headache | 16% | 21% | 28% | 7% |
| Flushing | 10% | 19% | 18% | 2% |
| Dyspepsia (upset stomach) | 3% | 9% | 17% | 2% |
| Abnormal vision | 1% | 2% | 11% | 1% |
| Nasal congestion (stuffy nose) | 4% | 4% | 9% | 2% |
| Back pain | 3% | 4% | 4% | 2% |
| Myalgia (muscle pain) | 2% | 2% | 4% | 1% |
| Nausea | 2% | 3% | 3% | 1% |
| Dizziness | 3% | 4% | 3% | 2% |
| Rash | 1% | 2% | 3% | 1% |
Sources: Viagra (sildenafil) label, Table 1 (reactions reported by ≥2% of patients and more often than placebo, fixed-dose phase II/III studies). Accessed Oct 28, 2026.
How to read this: these are the percentages of trial participants reporting each reaction, not your personal odds. The Viagra (sildenafil) label also reports flexible-dose trials, in which men started at 50 mg and could adjust the dose; it says those studies reflect its recommended dosing regimen.
| Side effect | Viagra, flexible dose (N=734) | Placebo (N=725) |
|---|---|---|
| Headache | 16% | 4% |
| Flushing | 10% | 1% |
| Dyspepsia (upset stomach) | 7% | 2% |
| Nasal congestion (stuffy nose) | 4% | 2% |
| Abnormal vision | 3% | 0% |
| Back pain | 2% | 2% |
| Dizziness | 2% | 1% |
| Rash | 2% | 1% |
Source: Viagra (sildenafil) label, Table 2 (reactions reported by ≥2% of patients and more often than placebo, flexible-dose phase II/III studies of 2 to 26 weeks). Accessed Oct 28, 2026.
The Viagra (sildenafil) label reports that 2.5% stopped treatment because of adverse reactions versus 2.3% taking placebo; that does not mean only 2.5% experienced a side effect.
For dosing basics, forms and cost, start with our main sildenafil (Viagra) guide. If you are wondering about taking more, read how much Viagra is too much.
Can Viagra cause headaches?
Yes. Headache is the most common side effect of Viagra. In the fixed-dose trials in the Viagra (sildenafil) label, it was reported by 16% of men at 25 mg, 21% at 50 mg and 28% at 100 mg, versus 7% on placebo; in the flexible-dose trials, by 16% versus 4%. The label notes that in fixed-dose studies the incidence of some adverse reactions increased with dose.
Why does Viagra cause headaches?
The Viagra (sildenafil) label does not name a single cause. It says PDE5, the enzyme sildenafil blocks, is also found in vascular smooth muscle, that blocking it may underlie peripheral arterial-venous dilatation, and that sildenafil “has systemic vasodilatory properties” that briefly lowered blood pressure in healthy volunteers.
Why does this matter for a sildenafil headache? A small placebo-controlled migraine study on PubMed found evidence for a cGMP-dependent mechanism without initial widening of the middle cerebral artery. The mechanism is more complex than simply “blood vessels widen”; the Viagra (sildenafil) label establishes that headache is a recognized reaction, but does not identify its precise cause.
What to do about a Viagra headache
- Ask your prescriber about the dose. The Viagra (sildenafil) label says the dose may be “decreased to 25 mg” based on effectiveness and toleration. Do not take extra or a second dose the same day; see how much Viagra is too much.
- Report headaches that persist. The Viagra (sildenafil) label says: “Tell your healthcare provider if you have any side effect that bothers you or does not go away.”
- Mention alcohol and other medicines. The Cialis (tadalafil) label warns that substantial alcohol (e.g., 5 units or greater) with tadalafil can increase dizziness, headache and drops in standing blood pressure. The Viagra (sildenafil) label does not recommend a specific pain reliever, so ask your prescriber or pharmacist before adding one.
How long does a Viagra headache last?
The Viagra (sildenafil) label does not report how long headaches lasted in its trials. It does state that sildenafil and its active metabolite have terminal half-lives of about 4 hours, and that peak blood levels are reached within 30 to 120 minutes (median 60 minutes) on an empty stomach. A half-life describes declining drug levels; it is not a four-hour deadline for symptoms to end. Tell your provider about symptoms that bother you or do not go away, as the label instructs.
When a headache comes with warning signs
Get help right away if a headache comes with any of these, which the Viagra (sildenafil) label patient information lists: “chest pain, dizziness, or nausea during sex” (stop sexual activity; see Viagra and your heart); “sudden vision loss in one or both eyes”; “sudden hearing decrease or hearing loss”; or “an erection that lasts more than 4 hours.” If you take nitrates, the label says sildenafil “can cause your blood pressure to drop suddenly to an unsafe level”; see ED medication and nitrates.
Does Cialis cause headaches too?
Yes. The Cialis (tadalafil) label lists headache in 11% at 5 mg, 11% at 10 mg and 15% at 20 mg for as-needed use (5% on placebo), and in 3% at 2.5 mg and 6% at 5 mg for once-daily use (5% on placebo). Tadalafil’s mean terminal half-life is 17.5 hours in healthy subjects, per the same label. Both labels say rates from different drugs’ trials “cannot be directly compared.” See our tadalafil (Cialis) guide.
Headaches making you rethink your ED treatment? Start an online ED visit to share your side-effect history with an independent licensed provider. Prescription required.
Rare but serious side effects of Viagra: vision, hearing, priapism and blood pressure
Use the symptom to choose the next step. The Viagra (sildenafil) label gives the following warnings; postmarketing reports cannot reliably establish how often an event occurs or whether the medicine caused it.
| Warning | What the label says | What to do |
|---|---|---|
| Sudden vision loss in one or both eyes | Possible sign of NAION, which the Viagra (sildenafil) label calls rare; stop all PDE5 inhibitors | Stop the medicine and get medical care right away. See ED pills and your eyes. |
| Sudden decrease or loss of hearing | May come with ringing in the ears or dizziness; a causal link has not been determined (Viagra (sildenafil) label) | Stop the medicine and get prompt medical care. |
| Erection lasting more than 4 hours | Prolonged erections and priapism have been reported infrequently (Viagra (sildenafil) label) | Get emergency care; do not wait for it to pass. |
| Nitrates or riociguat | Use with organic nitrates/nitrites (including poppers) or riociguat is contraindicated (Viagra (sildenafil) label) | Never combine. See ED medication and nitrates. |
| Alpha-blockers and blood pressure | Additive lowering can cause symptomatic low blood pressure; the sildenafil starting dose is 25 mg once the patient is stable on the alpha-blocker (Viagra (sildenafil) label) | Tell the prescriber. See Viagra, Cialis and blood pressure. |
| Heart symptoms during sex | Not recommended when sexual activity is inadvisable for cardiovascular reasons; serious heart events were reported after marketing, mostly in men with prior risk factors (Viagra (sildenafil) label) | Stop sexual activity and get medical help right away for chest pain. See Viagra and your heart. |
Sources: Viagra (sildenafil) label; Cialis (tadalafil) label (same class warnings). Accessed Oct 28, 2026.
Do not wait for pain: the Viagra (sildenafil) label says, “If you have an erection that lasts more than 4 hours, get medical help right away.” Read our priapism guide for more on this warning; untreated priapism can cause permanent damage, per the same label.
The Viagra (sildenafil) label also notes that it is unknown when nitrates can be given safely after a sildenafil dose. If you ever need emergency treatment for chest pain, tell the team you took an ED medicine and when.
What each path includes
The Viagra (sildenafil) label directs you to report bothersome or persistent symptoms and seek immediate help for the warning signs above. Here is how to choose your next step.
| Your situation | Starting point | What it includes |
|---|---|---|
| Headache, flushing or stuffy nose that bothers you | Your current prescriber | Review of dose and timing; the Viagra (sildenafil) label lists a 25–100 mg range and says some reactions increase with dose. |
| Side effects that keep bothering you | Prescriber review of the medicine | Discussion of another PDE5 option such as tadalafil (see the Cialis (tadalafil) label) or a different approach. Prescription required. |
| Vision or hearing loss, erection over 4 hours, chest pain | Medical help right away | Immediate assessment; the Viagra (sildenafil) label says to stop and seek care. |
| Considering a new ED prescription | Mendoxa online assessment | Independent licensed providers review your health and medicines; the compounded tablet is not FDA-approved. |
Sources: Viagra (sildenafil) label; Cialis (tadalafil) label; FDA compounding Q&A; Mendoxa care information. Accessed Oct 28, 2026.
For a nonurgent treatment review, use the online visit to share your medicine list, the symptoms you experienced and when they occurred; the Viagra (sildenafil) label asks patients to disclose all prescription medicines, over-the-counter medicines and supplements. Compare ED medication options before the visit.
Could Mendoxa ED care fit you?
Online ED visit · Prescription required · Independent licensed providers · Not available in California
Other common side effects: upset stomach, stuffy nose, blue vision and back pain
Upset stomach
Dyspepsia rose from 3% at 25 mg to 17% at 100 mg in the Viagra (sildenafil) label fixed-dose table, versus 2% on placebo. As with headache, the label allows the dose to be adjusted based on toleration; ask your prescriber rather than changing it yourself.
Food changes timing. Sildenafil can be taken with or without food, but a high-fat meal can make it take longer to start working, according to the Viagra (sildenafil) label. That is not evidence that a heavy meal prevents side effects.
Viagra stuffy nose
A stuffy or runny nose is listed in the Viagra (sildenafil) label; nasal congestion rates appear in the dose table above. Tell your provider if it bothers you or persists, and include any over-the-counter medicines you use in your medication list, as the label instructs.
Blue vision: temporary changes versus sudden loss
The Viagra (sildenafil) label describes abnormal vision as usually a transient color tinge, light sensitivity or blurred vision; subjects also reported difficulty distinguishing blue from green. The 11% figure at 100 mg covers all abnormal vision, not blue vision alone.
Sudden vision loss needs immediate attention: stop sildenafil and contact a healthcare provider right away, as directed by the Viagra (sildenafil) label. Read ED pills and your eyes for the distinction between color changes and the NAION warning.
Back pain or muscle pain
Both appear in the Viagra (sildenafil) label. The Cialis (tadalafil) label says tadalafil-related back or muscle pain generally began 12 to 24 hours after dosing and typically resolved within 48 hours; that timing should not be assigned to sildenafil.
Alcohol and other ED medicines
The Cialis (tadalafil) label warns about substantial alcohol use with tadalafil (see the headache section above and ED and alcohol). The Viagra (sildenafil) label and Cialis (tadalafil) label advise against combining PDE5 inhibitors or adding other ED treatments because safety and effectiveness have not been studied; see Cialis and Viagra together.
Long-term side effects of Viagra: what the data show
The evidence supports continued tolerability in selected men, but it cannot promise that long-term use is risk-free. The Viagra (sildenafil) label reports that more than 550 patients were treated for longer than one year.
The 4-year sildenafil study on PubMed enrolled 979 men who had already completed earlier trials; 584 (60%) completed all 4 years. It recorded serious adverse events and events that led to dose changes or temporary or permanent discontinuation: 37 men (3.8%) had treatment-related events requiring a dose change or discontinuation, with none of those events serious. This endpoint is not a count of everyone who experienced a symptom; the Viagra (sildenafil) label remains the source for current warnings.
What this cannot tell you: an open-label extension of prior trial completers cannot settle the risk of rare harms or predict your individual experience. The Viagra (sildenafil) label warns that untreated priapism can cause permanent damage and includes sudden vision and hearing loss warnings; do not treat the long-term findings as a reason to wait out those symptoms.
Would switching to Cialis avoid side effects?
Headache can occur with either medicine. The Viagra (sildenafil) label and Cialis (tadalafil) label report rates from separate studies; those rates cannot establish which would suit you better. The tadalafil headache percentages are listed in the headache section above.
Before requesting a switch, tell the provider which symptom you had, when it started and which other medicines you take. For more about the alternative, read our tadalafil guide and sildenafil vs tadalafil comparison.
Bring your side-effect history to a Mendoxa ED visit
Use the Mendoxa online assessment to ask whether its compounded rapid-dissolve tablet fits your care. Independent licensed providers review your health and medicines. Prescription required; treatment depends on the provider’s assessment.
Mendoxa’s compounded tablet combines sildenafil, tadalafil and apomorphine and is not FDA-approved. Component labels flag risks to discuss: headache, vision changes and blood-pressure interactions in the Viagra (sildenafil) label; headache, indigestion and back pain in the Cialis (tadalafil) label; and nausea, dizziness and fainting in the APOKYN (apomorphine) label. Those separate-product rates do not establish the combination’s side-effect rates.
The APOKYN (apomorphine) label contraindicates apomorphine with 5HT3 antagonists such as ondansetron because profound low blood pressure and loss of consciousness have been reported. That label covers an injectable Parkinson’s treatment, not this compounded ED tablet; ask the provider to review the full ingredient list and alternatives with you.
Read about the combination ED tablet and Mendoxa ED care before starting. The table below shows the available quantities and costs.
Mendoxa ED plans and prices
Choose a quantity to discuss during your online visit. Prescription required; an independent licensed provider decides whether treatment is appropriate.
| Tablets per month | 1-month total | Per tablet (1 month) | 3-month total | Per tablet (3 months) |
|---|---|---|---|---|
| 6 tablets / month | $129 | $21.50 | $329 | $18.28 |
| 10 tablets / month | $149 | $14.90 | $379 | $12.63 |
| 20 tablets / month | $179 | $8.95 | $449 | $7.48 |
The 3-month total covers three months at the monthly tablet quantity shown.
If prescribed · Cancel anytime · Available in 49 states (not California). Source: Mendoxa pricing supplied for this update, Oct 28, 2026. Confirm the current total during your online visit.
FAQ
What is the most common side effect of Viagra?
Headache. The Viagra (sildenafil) label reports it in 16% of men at 25 mg, 21% at 50 mg and 28% at 100 mg, versus 7% on placebo. Flushing is second.
Can Viagra cause headaches?
Yes. Headache is the most common side effect in the Viagra (sildenafil) label: 16% to 28% across 25–100 mg in fixed-dose trials versus 7% on placebo, and 16% versus 4% in flexible-dose trials. The label allows the dose to be decreased to 25 mg based on toleration, so ask your prescriber about a bothersome headache; get medical help right away if it comes with chest pain during sex, sudden vision or hearing loss, or an erection lasting more than 4 hours.
Does a Viagra headache mean it is working?
The Viagra (sildenafil) label lists headache as an adverse reaction, not a measure of treatment success. Tell your prescriber whether treatment helped and whether headache made it difficult to use; the label bases dose adjustment on both effectiveness and toleration.
How long do Viagra side effects last?
The Viagra (sildenafil) label does not give a duration for headache or most other common side effects. It reports that sildenafil and its active metabolite have terminal half-lives of about 4 hours. That describes drug clearance, not a guaranteed duration of symptoms. Tell your provider about any side effect that bothers you or does not go away; an erection lasting more than 4 hours, or sudden vision or hearing loss, needs medical help right away.
Does Viagra have long-term side effects?
The 4-year sildenafil study on PubMed supports continued tolerability in men who had completed earlier trials, but it cannot exclude rare harms or predict individual risk. The Viagra (sildenafil) label warns that untreated priapism can cause permanent damage and includes sudden vision and hearing loss warnings; long-term use does not remove those precautions.
Why does Viagra make things look blue?
The Viagra (sildenafil) label links temporary color-discrimination changes to sildenafil’s effect on retinal PDE6 and describes difficulty distinguishing blue from green. Its 11% rate at 100 mg is for all abnormal vision, not blue vision alone; sudden vision loss requires stopping the drug and getting medical help right away.
Can Viagra cause a stuffy nose?
Yes. The Viagra (sildenafil) label lists a stuffy or runny nose among the most common side effects: 4% at 25–50 mg and 9% at 100 mg, versus 2% on placebo.
Does 100 mg cause more side effects than 50 mg?
For several effects, yes. In the Viagra (sildenafil) label table, headache was 28% vs 21%, upset stomach 17% vs 9% and abnormal vision 11% vs 2% at 100 mg vs 50 mg. Dose changes should go through your prescriber.
Ready to see if the Mendoxa ED tablet fits you?
From $129/month if prescribed · Cancel anytime · Available in 49 states (not California)
How we wrote this
Written by the Mendoxa editorial team · Sources: DailyMed/FDA and PubMed (NIH). We checked the sources on Oct 28, 2026. The dose tables reproduce the Viagra (sildenafil) label without pooling studies. The Cialis (tadalafil) label describes a separate approved product; neither label establishes rates for a compounded combination. FDA states that compounded drugs are not FDA-approved.
Updated Oct 28, 2026. This page is general information, not medical advice. A licensed clinician decides what fits you.
References
- DailyMed: VIAGRA (sildenafil citrate) tablet, film coated, label revised 12/2017. Accessed Oct 28, 2026.
- DailyMed: CIALIS (tadalafil) tablet, film coated, label revised 3/2026. Accessed Oct 28, 2026.
- DailyMed: APOKYN (apomorphine hydrochloride) injection, label revised 6/2022. Accessed Oct 28, 2026.
- FDA: Compounding and the FDA, questions and answers. Accessed Oct 28, 2026.
- McMurray JG, et al. Long-term safety and effectiveness of sildenafil citrate in men with erectile dysfunction. 2007. PMID 18516312. Accessed Oct 28, 2026.
- Kruuse C, Thomsen LL, Birk S, Olesen J. Migraine can be induced by sildenafil without changes in middle cerebral artery diameter. Brain. 2003;126(1):241–247. Accessed Oct 28, 2026.
- Mendoxa ED care (product, format, max 1 dose per 24 hours). Accessed Oct 28, 2026.
- Mendoxa ED intake: confirm current prices. Accessed Oct 28, 2026.
About Mendoxa
Mendoxa (mendoxa.co) is a US telehealth brand. Independent licensed providers (licensed clinicians in the LocumTele network) review each online visit, and prescriptions are filled by Rush Pharmacy, a licensed US pharmacy. Available in 49 states (not California).
- Prescription required. A licensed clinician reviews every visit and can say no. A prescription is not automatic.
- A compounded medicine is not an FDA-approved finished product (FDA compounding Q&A).
- Plans: 1 month or 3 months, from $129. If prescribed · Cancel anytime · Available in 49 states (not California).
Compounded medication prescribed only if a licensed U.S. clinician decides it is appropriate. Not FDA-approved as a finished product. Not available in California. This site is not for emergencies. Call 911 if you need urgent care.