I took 50 mg after a big dinner and nothing happened. Is it useless for me?
Six 50 mg tablets at four counters, and what the review threads get right
Figures below cover the middle strength at licensed US counters. This page is a reference and sells nothing.
| Pharmacy | Strength / count | How the window works | Official page |
|---|---|---|---|
| Publix | 50 mg x 6 | Supermarket pharmacy counter | Publix pharmacy |
| Costco | 50 mg x 6 | Warehouse pharmacy; membership may apply | Costco pharmacy |
| Walgreens | 50 mg x 6 | Ordinary cash counter | Walgreens pharmacy |
| H-E-B | 50 mg x 6 | Texas grocery pharmacy counter | H-E-B pharmacy |
Fifty milligrams in a pack of six is the count quoted below, at Publix, Costco, Walgreens and H-E-B, because 50 mg is the strength most first prescriptions carry. Published cash figures move with ZIP code and with the month; read them as a prompt to ring the pharmacy, since nobody honours a figure printed on a web page. Generic sildenafil has been on the US market since December 2017, several manufacturers make it, and brand Viagra sits well above the generic - so a surprising number at the counter is worth querying before it gets paid.
Row links open each chain's own pharmacy page. Coupon services publish their own figures for the same strength and are credited in the caption, since a discount figure and a shelf figure describe different transactions.
Review pages are reliable on one point and thin on another. What recurs across them - 50 mg satisfies most men, 100 mg works somewhat better while producing more headache and flushing, 25 mg often reads as too cautious - matches the trial data further down. What those pages rarely explain is why a particular man was started at 25 mg, which is a clearance question and not a severity one.
Every strength needs a prescription in the United States, telehealth included, and no over-the-counter version exists in that market.
Sixty minutes fasted, an extra hour after a fatty meal
Most complaints that the tablet did nothing come down to how the evening was run.
Fasted, absorption is quick. Maximum plasma concentrations arrive within 30 to 120 minutes, median 60, and mean absolute bioavailability is about 41 percent with a range of 25 to 63. That median is where the advice to allow an hour comes from. A high-fat meal shifts the rate rather than the total: Tmax out by a mean of 60 minutes, Cmax down by a mean of 29 percent, AUC down only about 11 percent - which is why pharmacology texts describe the food effect as clinically minor. It does not read as minor to a man who swallowed 50 mg twenty minutes after a steak and spent the evening deciding the drug had failed him.
Two hours after a heavy meal, or before the meal instead of after it. That is the entire instruction.
One or two drinks change little. A long session lowers blood pressure a bit further and dulls arousal, and without arousal there is no nitric oxide signal for sildenafil to protect.
Three strengths, and the list of men who open at 25 mg
Three tablet strengths, and the choice between them turns mostly on how fast a given man clears the drug.
| Strength | Usually started for | Notes |
|---|---|---|
| 25 mg | Age 65+, liver disease, CrCl under 30, strong CYP3A4 inhibitors, alpha-blocker start | Can be stepped up later if tolerated |
| 50 mg | Most adults with erectile dysfunction | The strength quoted in the counter figures above |
| 100 mg | Men who responded poorly to a fair run at 50 mg | Ceiling for ED; headache and flushing more frequent |
| Revatio 20 mg | Pulmonary arterial hypertension | Three times daily under specialist care, not an ED substitute |
Fifty milligrams is the usual adult dose, moved to 100 mg or down to 25 mg once there is something to judge. One dose in any 24 hours at every strength.
Twenty-five milligrams goes to men in whom the drug will run high, which is a different thing from mild disease. The label's list: age 65 and over, hepatic impairment such as cirrhosis, severe renal impairment with creatinine clearance under 30 mL/min, and erythromycin or a strong CYP3A4 inhibitor such as ketoconazole, itraconazole or saquinavir. Alpha-blockers sit alongside with an extra condition attached. The man is stable on the alpha-blocker first, then sildenafil starts at 25 mg, because two vasodilators arriving on the same evening is how people end up on the bathroom floor.
Ritonavir is its own case and the numbers explain why. Co-administration raised sildenafil AUC elevenfold and Cmax fourfold, and 24 hours after a dose plasma levels were still around 200 ng/mL against roughly 5 ng/mL when sildenafil was given alone. The label therefore caps it at a single 25 mg dose in any 48-hour period. That is the one interaction here which changes the interval and not only the number on the tablet.
One hundred milligrams is the ceiling for erectile dysfunction and it arrives later. The fixed-dose adverse-event table shows what the last step costs: headache 16, 21 and 28 percent at 25, 50 and 100 mg against 7 percent on placebo; flushing 10, 19 and 18 against 2; dyspepsia 3, 9 and 17 against 2. Real gain in response, real gain in nuisance.
A fair trial: adequate dose, an hour's notice, real arousal
One failed evening is not a verdict on the drug, and two are not either.
Around eight properly timed attempts is the figure clinics use before calling sildenafil ineffective. Most men who abandon it stop after one or two evenings, and the evenings usually explain themselves: a late heavy dinner, no waiting time, too much wine, a room with an argument still in it. Milligrams fix none of that. Doubling the dose after a bad Friday reliably adds headache and settles nothing.
Where a properly used 50 mg dose fails repeatedly, that is a review. The prescriber can step to 100 mg or look again at testosterone, vessels, diabetes, depression or the relationship - the ground covered in why an erection fails. There is decent trial evidence for the harder groups too: in men with diabetes, 57 percent reported improved erections against 10 percent on placebo, with 48 percent of attempts successful against 12.
A different complaint arrives in the same postbag from couples who resent planning an hour ahead. That is a question of fit, and the tadalafil page covers both of its dosing patterns.
Blue-green vision, PDE6, and the two symptoms that end a prescription
A tinge that comes and goes is expected on this drug. Vision or hearing that disappears is not.
Sildenafil, the short chemical picture
| Property | Sildenafil |
|---|---|
| Drug class | PDE5 inhibitor |
| Salt in tablets | Sildenafil citrate |
| Plasma protein binding | About 96 percent, parent and metabolite |
| Volume of distribution | About 105 L at steady state |
| Main metabolite | N-desmethyl, about 50 percent of parent potency |
| PDE5 over PDE6 selectivity | About tenfold - the basis of the colour effect |
| Excretion | Mostly faecal; about 13 percent urinary |
The ordinary effects are vascular and dull: headache, flushing, dyspepsia, nasal congestion, back pain, myalgia, nausea, dizziness, mild visual change. They run on the same four to six hour clock as the wanted effect and turn up more often at 100 mg than at 25 mg.
The visual complaint men write in about is a blue or blue-green tinge, sometimes lights that look harsher than usual. Sildenafil is only about tenfold selective for PDE5 over PDE6, the retinal enzyme in the phototransduction pathway, and that narrow margin is the accepted explanation. At single doses of 100 and 200 mg, the Farnsworth-Munsell 100-hue test picked up transient dose-related impairment of colour discrimination, peaking near peak plasma levels; visual acuity, intraocular pressure and pupillometry were unaffected at up to twice the maximum recommended dose. The men worth flagging before a 100 mg prescription are the ones whose work depends on colour - electricians, printers, pilots. A tinge lasting four hours is harmless in a bedroom and expensive on a shift.
Sudden loss of vision in one or both eyes means stopping the tablet and being seen the same day, because NAION presents that way. Sudden hearing loss, with or without tinnitus, gets the same response. Neither has anything in common with the tinge above, and neither is a wait-and-see symptom. An erection past four hours is an emergency, since priapism damages tissue permanently, and sickle cell disease and other predisposing conditions carry that warning at the front of the label.
Age, organ disease, and the shorter list that stops the drug
Two lists run in parallel here, and men routinely confuse them: one changes the dose, the other cancels the drug.
Age and a struggling liver change the starting dose. They do not stop the prescription. The list that stops it is much shorter: a nitrate anywhere on the medicine list, riociguat, known hypersensitivity, or a heart in a state where sex itself is unwise - recent infarct, unstable angina, uncontrolled arrhythmia, blood pressure nobody has yet got hold of. Fitness for sex is assessed before fitness for the tablet, with two flights of stairs the usual rough test.
Severe renal impairment raises the metabolite more than the parent: N-desmethyl AUC up 200 percent and Cmax up 79 percent against normal renal function. Hence a 25 mg start in that group.
Dr Marc Vidal reviewed this page. In clinic he asks three things: what else is on the list, when the last nitrate of any kind was taken, and what happened on the evenings that did not work. His notes are on the reviewer page. Bring the actual packets, because remembered drug names are wrong often enough to matter on a drug where one missed line is the whole risk.
Nitrates, poppers, riociguat and the 24-hour figure
This is the part of the page with no flexibility anywhere in it.
Nitrates in any form are a contraindication: nitroglycerin sprays, ointments and patches, isosorbide taken on a schedule, and the amyl or butyl nitrite poppers bought recreationally. Both groups widen vessels through the same pathway, and together they can cause a profound fall in blood pressure with syncope, infarction or stroke behind it.
There is no smaller dose that makes this safe and no later hour on the same evening. Where a nitrate becomes necessary in an emergency, at least 24 hours must have passed since the last sildenafil dose, and that call belongs to the team treating the emergency. What they need from the patient is the hour of the last tablet.
Riociguat, a guanylate cyclase stimulator used in pulmonary hypertension, is contraindicated on the same mechanism. Antihypertensives and alpha-blockers are permitted with care, and the doxazosin interaction studies are where that care comes from: stable on the alpha-blocker first, sildenafil at 25 mg, doses separated if standing up brings on dizziness. Chest pain during sex after a dose is never treated from a nitrate supply at home. That is a call to emergency services with the drug name and the hour in the first sentence.
Revatio 20 mg: the same molecule for a different illness
One molecule, two licences, two schedules. The bottles are not interchangeable in either direction.
Revatio is sildenafil licensed for pulmonary arterial hypertension, usually 20 mg three times a day under specialist supervision, aimed at smooth muscle in the lung arteries. Generic Revatio also exists as a 10 mg/mL oral suspension and as an intravenous form given by a clinician.
Households swap the boxes because the drug name matches, and both directions are wrong. A 20 mg lung tablet on a three-times-daily schedule is not a convenient small erectile dysfunction dose, and a leftover 50 mg does not stand in for a pulmonary hypertension regimen. Adding an occasion tablet on top of Revatio simply stacks vasodilation on someone already being treated with it.
Adcirca and Alyq are the tadalafil equivalents, and the same rule holds for them. Where erectile dysfunction and pulmonary hypertension exist in the same man, the two prescribers need to speak to each other, and that conversation does not happen in a comment thread.
Onset, peak, and a half-life of about four hours
Two numbers answer most of the questions here: about an hour to the peak, about four hours to clear half of it.
Sildenafil pharmacokinetics at a glance
Available strengths25, 50 and 100 mg
Time to peak, fasted30-120 minutes, median 60
BioavailabilityAbout 41 percent, range 25-63
Half-lifeAbout 4 hours
High-fat mealTmax +60 minutes, Cmax -29 percent, AUC -11 percent
ClearanceCYP3A4 major, CYP2C9 minor
Nitrate interval24 hours after the last dose
Onset is commonly 30 to 60 minutes, the peak sits near the hour mark fasted, and the terminal half-life is about four hours. That leaves a useful window of roughly four to six hours with a weaker tail behind it. The RigiScan work put a figure on the fade: an effect was still present at four hours, but diminished compared with two.
Clearance runs mainly through CYP3A4, with CYP2C9 taking a minor share. The N-desmethyl metabolite has about 50 percent of the parent's in vitro potency for PDE5, circulates at roughly 40 percent of parent concentrations, and accounts for about 20 percent of the pharmacological effect - which is why inhibitors of that enzyme matter more than a single figure suggests. Grapefruit belongs in the same conversation, well below a prescription inhibitor in strength. A litre-a-day habit is worth mentioning at the appointment; an occasional glass is no way to make the tablet stronger, and men who try it that way collect the side effects instead of the effect.
The age adjustment has hard numbers behind it. In healthy volunteers of 65 and over, sildenafil AUC ran about 84 percent higher than in men of 18 to 45 and the active metabolite about 107 percent higher; because protein binding differs with age, free fractions were up 45 and 57 percent. That is a wide enough gap to halve the starting dose.
Tablets that never went past a pharmacy counter
Everything above assumes a tablet dispensed against a prescription. A large share of the sildenafil sold online never was, and seizure analyses keep reporting the same three faults: too little drug, no drug, or something extra that nobody declared. Regulators publish the same warning about supplements sold for erections which turn out to contain undeclared sildenafil, and that is a specific danger for the man on nitrates who believes he bought a herbal capsule.
None of it is visible on the blister.
So the close is unremarkable. Get the prescription, keep the packets, take them to whoever adjusts the dose. If late dinners are the recurring obstacle, read the tadalafil page; if colour vision at 100 mg is what spoils it, vardenafil is the option to raise in clinic.
Last Updated
Straight talk
Your questions, answered plainly
Answered by Dr. Marc Vidal, MD · Internal medicine & clinical pharmacology
More readers write in about sildenafil than about anything else on this site, and the majority of those letters describe a clock rather than a dose. The answers below are general education, not advice for the person who sent them.
Probably not, and I would look at the dinner before the dose. A high-fat meal delays the peak by a mean of an hour and lowers it by about 29 percent, so a tablet swallowed twenty minutes after a steak is working uphill for most of the evening. Try again on a light stomach, roughly an hour ahead, with proper stimulation, and give it several separate attempts before drawing any conclusion - up to eight is the number clinics use. If a well-timed 50 mg dose still does nothing after that, go back to your prescriber rather than doubling the dose yourself, because doubling reliably adds headache and rarely adds anything else.
Why does the page cover three strengths instead of one number?
Because the label allows all three and men do not all start in the same place. The usual adult opening dose is 50 mg, which is also the strength in the counter figures at the top. Twenty-five is used where levels are expected to run high: age 65 and over, liver disease, severe kidney impairment, strong CYP3A4 inhibitors, or a recently started alpha-blocker. One hundred is the ceiling and comes after 50 mg has had a fair run. Revatio 20 mg is a lung dose on a three-times-daily schedule and does not belong in that sequence at all, whatever the arithmetic looks like.
How long does it last? He thinks one tablet covers the whole night.
It does not. The half-life is about four hours and the useful window is roughly four to six, with the peak near an hour if he has not just eaten a large meal. The trial work showed an effect still present at four hours but weaker than at two. It is an occasion tablet. If he wants something still working the next morning, that is tadalafil's profile, and no amount of sildenafil will imitate it. Neither drug is stronger than the other; they suit different weeks. The timing briefing goes through the numbers properly.
He said the room looked slightly blue. Should we stop?
A passing blue or blue-green tinge is a known effect. Sildenafil is only about tenfold more selective for PDE5 than for PDE6, the enzyme in the retina, and colour discrimination measured on the Farnsworth-Munsell test does shift transiently at 100 and 200 mg. It is dose-related, it is temporary, and it clears as the drug does. Knowing about it in advance usually turns a scare into a shrug. What does not belong in that category is sudden loss of vision in an eye, which needs the tablet stopped and same-day assessment. Sudden hearing loss needs the same. If the tinge bothers him every time, ask about a lower strength.
We sometimes use poppers. Can they be on the same night as sildenafil?
No. Poppers are nitrites and behave like the nitrates prescribed for angina. Combined with sildenafil they can cause a dangerous fall in blood pressure, with fainting and worse behind it. A smaller dose does not make it safe, and neither does spacing the two a few hours apart on the same evening; the labelled interval is 24 hours and it exists for emergencies rather than for planning. If poppers are part of your evenings, say so to the prescriber. They have heard it before and it changes the advice they give. The FDA drug pages at https://www.fda.gov/drugs carry the same warning in plainer wording.
My aunt takes Revatio for her lungs. Can he use one of hers if we run out?
No. Revatio is sildenafil for pulmonary arterial hypertension, usually 20 mg three times a day under specialist supervision. Viagra tablets are 25, 50 or 100 mg taken before an occasion. He should not dose erectile dysfunction out of her lung supply, and she should not use his 50 mg for lung pressure. Extra sildenafil on top of Revatio is simply more vasodilation in somebody already being treated with it, and her regimen is timed for a reason. Two conditions in one household means two prescribers rather than one shared cabinet.
The first two Fridays were hit and miss. Should I jump to 100 mg?
Not yet, and do not give up either. Early misses are common and usually have a fixable cause: a late dinner, no waiting time, a tense evening. A fair trial means an adequate dose, a light stomach, about an hour of head start and real arousal, repeated several times. Going to 100 mg after two awkward nights buys headache and flushing without proving anything about the drug. If a proper run at 50 mg fails, that is the point to see the prescriber, who can step the dose or look again at the cause. Why an erection fails covers the wider picture.
He is 68 and on a blood pressure tablet. What dose would you expect?
Twenty-five milligrams rather than fifty, in most cases. Clearance slows with age; exposure in men of 65 and over runs roughly 84 percent higher than in younger volunteers, and the free fraction is up about 45 percent because protein binding differs too. His antihypertensive already lowers blood pressure and sildenafil lowers it a little more, so starting low avoids the dizzy stand-up. If that tablet is an alpha-blocker, the doses get separated as well and he needs to be stable on it first. None of this bars him from treatment. The one thing that would is a nitrate anywhere on his list.
I read about NAION. How worried should I be?
Worried enough to know the warning sign, not worried enough to refuse a treatment your clinician thinks is reasonable. NAION is a rare, sudden event affecting the optic nerve, and most reported cases had vascular or anatomical risk factors already present - a crowded optic disc, age over 50, diabetes, hypertension, coronary disease, smoking. Sudden loss of vision in one or both eyes means stopping sildenafil and being seen urgently. It is a separate thing from the temporary blue tinge, which comes from PDE6 and fades. Men who have already had NAION in one eye need that discussed specifically in clinic.
He drinks a lot of grapefruit juice. Does that matter?
It can. Grapefruit inhibits CYP3A4, the enzyme that clears most of the sildenafil, so levels run a little higher than expected. A daily habit is worth mentioning at the appointment; an occasional glass is not something to plan around, and it is certainly not a way to boost the tablet on purpose. Prescription inhibitors are the serious version of the same problem, and ritonavir is the extreme case: an elevenfold rise in exposure, and a label limit of 25 mg in any 48 hours. Erythromycin, ketoconazole and itraconazole put him on a 25 mg starting dose. The light-stomach advice still applies either way.
Which of the four pharmacies in the table should I use from Catalonia?
None of them. Publix, Costco, Walgreens and H-E-B are US counters, quoted here so a reader can see what a generic 50 mg pack of six costs inside that market. They do not ship to Spain, and this site dispenses nothing at all. If you are in Catalonia the route is a local prescription and a local farmacia. The table is for comparison, and every link goes to the chain's own pharmacy page so nobody is quietly sent to a coupon site instead. I am not going to invent a euro figure for your street either.
Is the blue tinge more likely on 100 mg than on 25?
Yes, it is dose-related, and most men who notice it are on the highest strength. Dropping down often settles it without abandoning the drug, and the tinge fades along with the drug across the four-hour half-life. It changes none of the other advice: still about an hour ahead, still a light stomach. If his job depends on exact colour - wiring, print, flying - mention it before anyone writes 100 mg. Vardenafil acts less on that retinal enzyme, but switching is a clinic decision and not a swap from a leftover pack of somebody else's tablets.
We like late dinners and dislike planning. Are we on the wrong drug?
Quite possibly. Sildenafil wants a light stomach and an hour of notice, and neither of those fits a household that eats at eleven. Tadalafil is barely affected by food and leaves a window of about 36 hours, which suits couples who do not want to schedule anything. That is a lifestyle fit rather than a statement about potency, and the response rates across the class sit in one band. Read the tadalafil page and the daily versus on-demand briefing before writing off 50 mg for being short-acting. The nitrate rule applies to both, with a longer interval on tadalafil.
Read each reply as a general teaching point, not a plan built for the person who asked. Your own situation - notes, bloods, every medicine you take - belongs in front of a prescriber who can weigh all of it together.