Sildenafil Citrate: Uses, Doses and Forms for ED and Pulmonary Hypertension

Sildenafil citrate is one drug with two approved jobs. As Viagra, it treats erectile dysfunction with a single dose before sex. As Revatio, it treats pulmonary arterial hypertension (PAH), a serious disease of the lung arteries, with doses taken three times a day, in adults and in children from age 1. Most people only know the first. This guide covers both: what sildenafil citrate is, how the two uses differ in dose and form, what the trials behind each approval found, and the warnings that apply to every product that contains it.

The numbers come from the US prescribing information for Viagra and Revatio and from Drugs@FDA, all listed at the end.

The short answer

Sildenafil citrate is the citrate salt of sildenafil, a PDE5 inhibitor. Tablet strengths are stated as sildenafil itself, so a "100 mg" tablet contains about 140 mg of sildenafil citrate. For erectile dysfunction the usual dose is 50 mg as needed, at most once a day, up to 100 mg. For PAH in adults it is 20 mg three times a day, up to 80 mg three times a day, which can add up to 240 mg a day. In SUPER-1, the main trial of sildenafil on its own in PAH, it improved walking distance by 45 to 50 metres over placebo; added to epoprostenol in PACES-1, it cut clinical worsening from 19% to 6%. Both uses share the same absolute rule: never with nitrates or riociguat. And the two should not be combined: people taking Revatio should not also take Viagra or another PDE5 inhibitor.

What sildenafil citrate is

Sildenafil is the active molecule; the citrate is the salt form used in the tablets and suspension. The labels express strength as sildenafil: "sildenafil citrate equivalent to 100 mg of sildenafil". The Revatio oral suspension label shows the ratio directly: 1.57 g of sildenafil citrate is equivalent to 1.12 g of sildenafil, so the citrate weighs about 1.4 times the base.

Sildenafil blocks PDE5, the enzyme that breaks down cGMP, a messenger that relaxes smooth muscle in blood vessel walls. According to the Revatio label, it is about 4,000 times more selective for PDE5 than for PDE3 (involved in heart muscle contraction) but only about 10 times more selective than for PDE6, a retinal enzyme. That limited PDE6 selectivity is thought to explain the colour-vision changes seen at higher doses.

How the body handles sildenafil

The pharmacology is the same whichever brand name is on the box. Both labels give the same figures: about 41% of an oral dose reaches the bloodstream (range 25% to 63%), and peak levels arrive 30 to 120 minutes after a dose on an empty stomach, with a median of 60 minutes. A high-fat meal delays the peak by about an hour and lowers it by 29%. Sildenafil is broken down in the liver, mainly by CYP3A4 with a smaller role for CYP2C9, into an active metabolite that accounts for about 20% of the effect. Both have a half-life of about 4 hours, and about 80% of a dose leaves in the faeces as metabolites.

Two groups clear it more slowly. In healthy adults over 65, blood levels were 84% higher than in younger adults, and severe kidney impairment roughly doubled exposure. In PAH patients, steady-state levels were 20% to 50% higher than in healthy volunteers. This is why the erectile dysfunction label suggests starting older men at 25 mg.

Two approved uses, two brands

	Viagra	Revatio
Condition	Erectile dysfunction	Pulmonary arterial hypertension (WHO Group I)
FDA approval	27 March 1998	3 June 2005 (adults); children 1 to 17 years added later
How it helps	Allows an erection in response to sexual stimulation	Relaxes lung arteries to improve exercise ability and delay worsening
Forms	Tablets 25, 50, 100 mg	Tablets 20 mg; oral suspension 10 mg/ml (brand discontinued, generics available); injection 10 mg per 12.5 ml
Usual adult dose	50 mg as needed, once a day at most	20 mg three times a day
Maximum adult dose	100 mg once a day	80 mg three times a day
Who takes it	Men	Adults and children of either sex (75% of the main adult trial's patients were women)

Generic versions of both are widely available. Our generic Viagra guide covers who makes them and what they cost.

Dosing compared

The same molecule is used very differently. For erectile dysfunction it is taken once, about an hour before sex, only when needed. For PAH it is taken every day, three times a day, to keep a steady effect on the lung arteries.

Use	Dose	Total per day
Erectile dysfunction, usual	50 mg once, as needed	50 mg
Erectile dysfunction, maximum	100 mg once, as needed	100 mg
PAH in adults, usual	20 mg three times a day	60 mg
PAH in adults, maximum	80 mg three times a day	240 mg
PAH, intravenous	10 mg three times a day	30 mg

For children with PAH, the Revatio label gives 10 mg three times a day up to 20 kg, and 20 mg three times a day above 20 kg, with up to 40 mg three times a day for those over 45 kg if needed. Safety and effectiveness below 1 year of age have not been established.

Sildenafil for erectile dysfunction

For erectile dysfunction, the Viagra label's usual dose is 50 mg about an hour before sex (anywhere from 30 minutes to 4 hours), adjusted to 25 mg or 100 mg, no more than once a day. A 25 mg start is advised for men over 65, men with liver impairment or severe kidney impairment, and men taking certain interacting drugs; men on ritonavir should not exceed 25 mg in 48 hours. It works only with sexual stimulation.

Our sildenafil for erectile dysfunction guide covers the trial evidence by dose and by cause of ED, how to take sildenafil safely covers interactions, and how long sildenafil lasts covers onset and duration.

Sildenafil for pulmonary arterial hypertension: the evidence

In PAH, the arteries in the lungs narrow and stiffen, forcing the right side of the heart to work harder. Sildenafil relaxes those arteries. The key trials in the Revatio label:

• SUPER-1 (277 adults, 12 weeks): 20 mg, 40 mg or 80 mg three times a day improved the 6-minute walk distance by 45 to 50 metres more than placebo. The three doses did not differ from each other, indicating no extra benefit above 20 mg three times a day for that outcome.
• Study A1481324 (385 adults, long term): compared 5 mg, 20 mg and 80 mg three times a day. The 80 mg dose delayed clinical worsening compared with 5 mg (an unapproved dose used as the comparison), and estimated 3-year survival was 66%, 79% and 85% in the three groups. The label cites this study as the reason the adult dose may go up to 80 mg three times a day.
• PACES-1 (267 adults already on intravenous epoprostenol, 16 weeks): adding sildenafil improved walking distance by 26 metres over placebo, lowered mean pulmonary artery pressure by 3.9 mmHg, and more than doubled the share improving by at least one functional class (36% against 14%).
• Study A1481243 (103 adults on bosentan): adding sildenafil 20 mg three times a day did not improve walking distance.

Fewer patients got worse on sildenafil

In PACES-1, a clinical worsening event (death, lung transplant, hospital admission for PAH, or a treatment change because of deterioration) happened to 23 of 131 patients on placebo (18.7%) and 8 of 134 on sildenafil (6.2%). The label says placebo patients were 3 times more likely to have such an event. There were 4 deaths on placebo (3 of them as the first worsening event) and none on sildenafil.

PACES-1 (16 weeks)	Placebo + epoprostenol	Sildenafil + epoprostenol
Patients	131	134
Any clinical worsening	23 (18.7%)	8 (6.2%)
Death (first event)	3	0
Hospital admission for PAH (first event)	9	8

Children with pulmonary hypertension

Revatio is approved for PAH in children aged 1 to 17. In the STARTS-1 trial of 234 children, peak oxygen uptake improved by 6% to 13% across sildenafil doses against 0.5% on placebo; the combined comparison narrowly missed statistical significance, while the medium dose group differed from placebo. Pulmonary vascular resistance fell with the medium and high doses.

The label also reports an imbalance in deaths during the long-term pediatric studies, rising with dose: 9.1%, 13.5% and 22% in the low, medium and high dose groups, all related to progression of PAH. An adult study designed to test this risk (A1481324) did not confirm it, and the label concludes that a causal link is unlikely. It states that no maximum pediatric dose has been identified and allows up to 40 mg three times a day for children over 45 kg if needed. Pediatric dosing belongs with a specialist team.

Side effects in each use

The side effects are the same type in both uses, but the rates differ between the trials, which enrolled different patients taking different schedules. In SUPER-1:

Side effect (SUPER-1, 12 weeks)	Placebo	20 mg x3	40 mg x3	80 mg x3
Headache	39%	46%	42%	49%
Flushing	4%	10%	9%	16%
Indigestion	7%	13%	8%	13%
Muscle pain	4%	7%	6%	14%
Diarrhoea	6%	9%	12%	10%

Overall discontinuation rates were 3% at 20 mg and 40 mg, 8% at 80 mg, and 3% on placebo. In erectile dysfunction, the Viagra label's fixed-dose trials reported headache in 16%, 21% and 28% at 25, 50 and 100 mg, flushing in 10% to 19%, and abnormal vision in 11% at 100 mg.

Nosebleeds in pulmonary hypertension

The Revatio label singles out nosebleeds. They occurred in 13% of patients with PAH linked to connective tissue disease, but were barely above placebo in idiopathic PAH (3% against 2%). They were also more common in sildenafil patients taking a vitamin K antagonist such as warfarin: 9%, against 2% in those not taking one. The safety of sildenafil in people with bleeding disorders or active stomach ulcers is unknown.

Forms of sildenafil citrate

• Tablets: 25, 50 and 100 mg (erectile dysfunction) and 20 mg (PAH), all widely available as generics.
• Oral suspension: 10 mg per ml for PAH, made up from powder with 90 ml of water; the reconstituted suspension expires after 60 days. The Revatio brand suspension is discontinued in the US; generic versions remain.
• Injection: 10 mg per 12.5 ml vial for PAH, given as an intravenous bolus three times a day; a 10 mg intravenous dose is predicted to match a 20 mg oral dose.
• Oral film: Vybrique (25, 50, 75, 100 mg), approved in the US on 16 December 2025 for erectile dysfunction.
• Jellies, chewables and effervescent tablets: sold by Indian manufacturers for export, such as Kamagra; not FDA approved. Our Kamagra types comparison covers them.

Rules that apply to every sildenafil product

• Never with nitrates in any form, regularly or occasionally, including nitroglycerin and poppers: the combination can cause a dangerous fall in blood pressure.
• Never with riociguat, another pulmonary hypertension drug.
• Not with another PDE5 inhibitor: the Revatio label tells patients not to take Viagra or other PDE5 inhibitors with it.
• Interacting drugs: ritonavir and other strong CYP3A4 inhibitors raise sildenafil levels sharply; alpha blockers and other blood pressure drugs add to its blood pressure effect.
• Urgent help for sudden vision loss, sudden hearing loss, or an erection lasting more than 4 hours.
• Heart health first for ED use: the Viagra label says erectile dysfunction treatments should not generally be used by men for whom sex is inadvisable because of their heart condition. There are no controlled data in men who had a heart attack, stroke or life-threatening arrhythmia in the last 6 months, men with resting blood pressure below 90/50 or above 170/110, or men with unstable angina; use in these groups needs caution and a doctor's decision.
• Not recommended in pulmonary veno-occlusive disease (it can worsen the heart and lungs) or, for Revatio, retinitis pigmentosa. In pulmonary hypertension caused by sickle cell disease, a trial found more vaso-occlusive crises needing hospital care on Revatio than on placebo, and benefit has not been established.
• Caution with low resting blood pressure, fluid depletion, severe left ventricular outflow obstruction, a deformed penis (angulation, Peyronie's disease) or conditions that predispose to priapism (sickle cell anaemia, multiple myeloma, leukaemia), and in anyone who has already had NAION, a type of sudden vision loss.
• Allergy: anyone with a known hypersensitivity to sildenafil must not take it.

Pregnancy and PAH

PAH itself carries serious risks in pregnancy. The Revatio label says limited published data do not report a clear association between sildenafil and major birth defects, miscarriage or adverse maternal or fetal outcomes, and animal studies at high doses showed no birth defects. Pregnancy decisions in PAH belong with a specialist team. Viagra is not approved for use in women.

Never self-treat pulmonary hypertension

Erectile dysfunction products such as Cenforce or Kamagra contain sildenafil, but they are not a substitute for Revatio. PAH needs a confirmed diagnosis, usually by right heart catheterisation, and specialist monitoring, and several PAH patients should not take sildenafil at all (for example with veno-occlusive disease). The dosing is also different: three times a day, every day. If you have unexplained breathlessness, see a doctor.

Generic availability and cost

Both uses are covered by cheap generics in the US. In September 2026, the Medicaid NADAC survey showed US pharmacies paying about 5 cents for a generic 20 mg tablet and 13 cents for a generic 100 mg tablet, against $83.72 for brand Viagra 100 mg. Our generic Viagra guide has the full price history.

Where SafeRxPills fits

SafeRxPills sells sildenafil citrate tablets for erectile dysfunction made in India, such as Cenforce 100 and Fildena 100. These are not FDA-approved products, and we do not offer sildenafil for pulmonary hypertension, which needs specialist care.

Sources

• REVATIO (sildenafil) tablets, oral suspension and injection, US prescribing information (Viatris), sections 1, 2, 3, 4, 5, 6, 7, 8, 11, 12 and 14. DailyMed
• VIAGRA (sildenafil citrate) US prescribing information, sections 2, 4, 5, 6.1, 8, 11 and 12. DailyMed
• Drugs@FDA: VIAGRA NDA 020895 (27 March 1998); REVATIO tablets NDA 021845 (3 June 2005); REVATIO injection NDA 022473; REVATIO oral suspension NDA 203109 (discontinued); VYBRIQUE NDA 210858 (16 December 2025).
• Centers for Medicare and Medicaid Services. National Average Drug Acquisition Cost (NADAC), 2026 file, as of 23 September 2026. data.medicaid.gov

This article is for information only and is not medical advice. Sildenafil is a prescription medicine. Pulmonary arterial hypertension must be diagnosed and treated by a specialist.