Questions this tray answers
Pia asks: How does Viagra work? Viagra is sildenafil citrate. Sexual stimulation releases nitric oxide, which raises cGMP. The tablet blocks PDE5 so that cGMP is not chopped as fast. Muscle relaxes and blood flows in. No stimulation, no effect.
Lutz asks: How does Cialis work? Cialis is tadalafil. It inhibits the same PDE5 enzyme after nitric oxide has started cGMP. Stimulation is still required. As-needed function versus placebo was labelled out to 36 hours.
Soren asks: Do ED pills work without arousal? No. The Viagra and Cialis labels both say there is no effect without sexual stimulation. The tablet keeps cGMP; it does not start nitric oxide.
Bea asks: Why can't I take Viagra with nitrates? Nitrates dump nitric oxide body-wide. Viagra blocks the enzyme that clears cGMP. Together they can drop blood pressure. The US carton contraindicates organic nitrates and nitrites in any form.
Quin asks: How long does it take for Viagra to work? The leaflet uses about 30 minutes to 4 hours if the man is excited. Fasted peak is 30 to 120 minutes, median 60. A 50 mg study put median erection at 27 minutes. A high-fat meal delays Tmax about 60 minutes.
Dara asks: How does Levitra work? Vardenafil, the Levitra-family tablet, also inhibits PDE5 after nitric oxide. Stimulation is still required. The milligram tray and the QT note live on the vardenafil page.
Milo asks: What does Viagra do? It enhances nitric oxide in the penis by blocking PDE5. It does not relax isolated corpus cavernosum on its own and does not create an erection from the tablet alone.
Tess asks: Does food affect how Viagra works? A high-fat meal delays Tmax by about 60 minutes and cuts Cmax by 29%. Cialis may be taken without regard to food.
Hugo asks: Is Cialis the same mechanism as Viagra? Yes at the enzyme. Both are PDE5 inhibitors that hold cGMP after nitric oxide. They differ in clock, food, daily use, and BPH, not in the target.
Wren asks: Is Viagra over the counter in the US? No. US Viagra and generic sildenafil stay prescription-only. UK Viagra Connect is a 50 mg pharmacy pack after an MHRA switch on 28 November 2017, sold after a pharmacist check.
Ida asks: How do you take Viagra? The label starts most men at 50 mg about one hour before sex, or from 30 minutes to 4 hours. It may rise to 100 mg or fall to 25. Once a day is the ceiling. Stimulation is still required.
Yara asks: How long does Viagra last? The patient leaflet uses about 30 minutes to 4 hours if the man is excited. Plasma half-life is about 4 hours. The longer duration review sits on the sildenafil page.
Bo asks: What is Viagra? Viagra is Pfizer's brand tablet of sildenafil citrate for erectile dysfunction, in 25, 50, and 100 mg. It blocks PDE5 after nitric oxide has started.
How Viagra blocks PDE5 after nitric oxide
How does Viagra work at the enzyme? Pfizer's tablet is sildenafil citrate, a selective inhibitor of cGMP-specific PDE5. DailyMed's mechanism line is the same on every reprint: nitric oxide is released in the corpus cavernosum during sexual stimulation; guanylate cyclase then raises cGMP; cGMP relaxes that smooth muscle and blood flows in. Sildenafil has no direct relaxant effect on isolated human corpus cavernosum. It only enhances nitric oxide by blocking PDE5, the enzyme that degrades cGMP there. The usual start is 50 mg about one hour before sex, or anywhere from 30 minutes to 4 hours. The milligram may rise to 100 or fall to 25. Once a day is the labelled ceiling. Tablet strengths on that carton are 25, 50, and 100 mg.
No stimulation means the tablet has nothing to keep
The Viagra sheet says sildenafil at recommended doses has no effect in the absence of sexual stimulation. EMA's Viagra EPAR repeats it: the nitric oxide / cGMP path has to be switched on first. The tablet does not invent desire and does not start the gas. If the nerves that release nitric oxide are quiet, PDE5 has no extra cGMP to hold. That is why a first try can look empty when the room never let the signal fire. The chemistry is on the label, not in a second milligram.
How Cialis works on the same enzyme
Cialis is tadalafil. The US label says nitric oxide from nerve endings and endothelium stimulates cGMP in smooth muscle; tadalafil inhibits PDE5 so more cGMP stays; blood flows into the corpus cavernosum. Because stimulation is required to start that local nitric oxide, tadalafil has no effect without it. As-needed Cialis starts at 10 mg, then 20 mg or 5 mg, and improved erectile function versus placebo up to 36 hours. A 20 mg stopwatch study recorded a significant response down to 16 minutes; 52% had a successful attempt within 30 minutes against 35% on placebo. Daily ED is 2.5 mg, or 5 mg, without regard to the hour of sex. BPH, and ED plus BPH, sit at 5 mg once a day. The Cialis sheet says not to stack it with another PDE5 inhibitor. Food is not a gate on that carton.
When the 50 mg tablet is labelled to work
The patient leaflet puts the useful window from about 30 minutes out to 4 hours, if the man is sexually excited. Fasted peak plasma sits between 30 and 120 minutes, median 60. A 50 mg onset study recorded median erection at 27 minutes (range 12 to 70); 71% by 30 minutes, 82% by 45. The usual advice is about one hour before sex. That clock is leftover of "how long does it take for Viagra to work," not the four-hour duration review that already lives on the sildenafil tray.
A cheeseburger delays the same tablet
The leaflet names a high-fat meal, a cheeseburger and french fries. Mean Tmax then slips 60 minutes and Cmax falls 29%. Nichols 2002 put oral bioavailability at 41% (36 to 47). Cialis may be taken without regard to food, which is the lived difference on the same enzyme, not a second mechanism.
PDE6 is why some men see a blue tint
Sildenafil is about 10-fold as potent on PDE5 as on PDE6, the retinal phototransduction enzyme. That leftover of selectivity is the temporary blue tinge or brightness some men notice. Tadalafil is about 700-fold more potent for PDE5 than PDE6 on the Cialis sheet, which is why that tint is less of a Cialis story. Headache and flush still come from PDE5 in vessels outside the penis. Vardenafil is the third oral tablet on this enzyme; its QT note is a different leftover and belongs on that tray.
Nitrates use the same nitric oxide path
Viagra potentiates the blood-pressure drop from organic nitrates and nitrites, regular or intermittent. The carton contraindicates nitric oxide donors in any form. Poppers sit in that same donor group on the EMA sheet. The chemistry is the one already named: extra nitric oxide plus a plugged PDE5 drain. Spacing and heart disease sit on ED and heart health. Which tablet to pick after the path is clear sits on choosing an ED pill.
US Viagra still needs a prescription
Hims and Ro both write that US Viagra and generic sildenafil have needed a licensed prescription since the 1998 approval. There is no legal over-the-counter US tablet. Drugs.com says the same gate for a legal online fill: a licensed clinician first, then a pharmacy. The MHRA, on 28 November 2017, moved UK Viagra Connect (sildenafil 50 mg) from POM to a pharmacy medicine, sold after a pharmacist check, not to men with severe heart, liver, or kidney disease. That UK P pack is not the US carton. Where a US counter fills 25, 50, or 100 mg sits on the sildenafil tray.
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