Sildenafil instructions for use, how to take?

This page is an instruction manual for the use of sildenafil and all generics based on it presented in the GENERICS catalog: Kamagra, Malegra, Cenforce, Fildena, Suhagra, Sildigra, and others. Their active ingredient is the same — sildenafil citrate. The mechanism of action, dosages, contraindications, and interactions are identical for all these drugs.

What is sildenafil

Sildenafil is an active substance from the group of PDE-5 (phosphodiesterase type 5) inhibitors. It was first approved by the FDA on March 27, 1998, under the brand name Viagra® (manufactured by Pfizer). It was the world's first oral drug for the treatment of erectile dysfunction (ED).[1]

Over the past 27 years, sildenafil has become the most studied drug in the history of sexual medicine. Thousands of clinical studies have been published, and it has been used by tens of millions of men worldwide in various patient groups — with diabetes, hypertension, after prostate surgery, and in the elderly. This volume of data makes it the "gold standard" for comparing new molecules.

Today, there are several hundred generics based on sildenafil on the market — including those presented in our catalog. A generic contains the same molecule in the same dosage, undergoes GMP production control, and costs several times less than the original. The difference is only in the price and auxiliary components (fillers, dyes), which practically do not affect the effectiveness of the drug.

How sildenafil works

Erection is a vascular process. During sexual arousal, nerve endings in the penis release nitric oxide (NO). NO triggers the synthesis of cyclic guanosine monophosphate (cGMP) — this is the substance that relaxes the smooth muscle of blood vessels, causing blood flow to the cavernous bodies and forming an erection.

The PDE-5 enzyme constantly destroys cGMP, limiting the duration of the erection. In erectile dysfunction, the activity of PDE-5 is excessive — cGMP is destroyed faster than it is produced, and the erection does not reach the required hardness or quickly weakens.

Sildenafil blocks PDE-5, allowing cGMP to accumulate and act longer. As a result, during sexual arousal, the vascular response becomes full-fledged. Key point: sildenafil does not cause an erection by itself — sexual arousal is necessary for it to work. Without it, the drug does not work.[2]

Scheme: during sexual arousal, nitric oxide is produced → triggers cGMP synthesis → relaxes blood vessels → erection. The PDE-5 enzyme destroys cGMP and dampens the process. Sildenafil blocks PDE-5, preventing cGMP from being destroyed prematurely.

Dosages

Sildenafil is available in dosages from 25 to 200 mg. The range is wide, and each step has its own logic of application.

25 mg — minimum dose

Recommended for elderly men (over 65 years old), patients with moderate hepatic or severe renal insufficiency, as well as those taking moderate CYP3A4 inhibitors (e.g., erythromycin). In such conditions, the clearance of sildenafil decreases, and the concentration of the drug in the blood is higher than in healthy middle-aged people. Starting with 25 mg allows assessing tolerability.

50 mg — recommended starting dose

It is with 50 mg that the official instructions for the original drug recommend starting. This is the dose received by most clinical trial participants. It is suitable for the first acquaintance with the drug and for most men with mild to moderate ED. If 50 mg provides a sufficient effect, there is no point in increasing the dose.

100 mg — standard therapeutic dose

The maximum officially recommended single dose. It is prescribed for an insufficient response to 50 mg. It is used by most men with moderate to severe ED. According to clinical data, it is at 100 mg that maximum effectiveness is achieved.[2]

150 mg and 200 mg — increased doses of generics

Doses above 100 mg are found only in generics — these are not officially recommended dosages, but a commercial decision of manufacturers. Their logic: some buyers split the tablet to save money, and 200 mg in this case costs like two doses of 100 mg. If you are prescribed a dose of 100 mg, do not switch to 150 or 200 mg on your own — the risk of side effects increases proportionally to the dose. The upper recommended dose according to FDA data is 100 mg per day.

The maximum frequency of administration is 1 time per day, regardless of the dosage.

How to take

Time of administration

The tablet is taken 30–60 minutes before planned sexual activity. Do not chew or crush. In clinical studies, in some patients, the effect was recorded as early as 14–25 minutes after taking on an empty stomach — this is due to individual absorption rates. The optimal "waiting window" for most men is about 45–60 minutes.[2]

What to wash down with: only clean non-carbonated water, a glass (~200 ml). Tannins in tea and coffee, carbon dioxide in carbonated drinks, and acid in citrus juices can unpredictably delay absorption. Grapefruit juice is separately contraindicated: it inhibits CYP3A4 in the intestine and increases the concentration of sildenafil in the blood.

Influence of food

Sildenafil is the most sensitive to fatty food among all PDE-5 inhibitors. A pharmacokinetics study (Muirhead et al.) showed: taking a 100 mg dose after a fatty meal delays reaching the peak concentration (Tmax) by about 60 minutes and reduces Cmax by about 29%.[3] This means that after a heavy fatty dinner, you will have to wait longer for the effect, and the effect itself may be less pronounced. For a predictable result, take the drug on an empty stomach or after a light snack. Light or moderate-fat food practically does not affect pharmacokinetics.

Alcohol

Moderate doses of alcohol are not an absolute contraindication, but they carry two risks. First, both alcohol and sildenafil lower blood pressure — their combined action can cause orthostatic hypotension (dizziness when standing up quickly), tachycardia, and headache. Second, alcohol itself suppresses erection through the central nervous system, meaning it works against the very effect for which the drug is taken. Practical recommendation: no more than 1–2 glasses of wine a few hours before taking. During the first few doses, abstain completely to understand your individual reaction.

Effectiveness

Clinical trial data (over 3700 patients aged 19–87 years) demonstrate the following picture:

Overall effectiveness

In placebo-controlled studies, sildenafil (25–100 mg) provided a significant improvement in erectile function on the IIEF scale compared to placebo. At doses of 50 and 100 mg, 63 to 82% of intercourse attempts were successful, compared to 20–24% in the placebo group.[2]

In diabetes mellitus

ED occurs in 50–75% of men with diabetes and is traditionally considered difficult to treat. In a randomized study (110 patients with type 2 diabetes, mean age 59 years, 12 weeks), sildenafil significantly improved rates of achieving and maintaining erection. Global efficacy question: "yes" was answered by 64.6% in the sildenafil group versus 10.5% in the placebo group. The drug worked even with poorly controlled diabetes and the presence of chronic complications.[4]

A meta-analysis of 8 RCTs (1172 patients) confirms: against the background of sildenafil, the relative risk of a positive response is 3.99 times higher than with placebo (95% CI: 2.58–6.18).[5]

After prostate surgery

After nerve-sparing radical prostatectomy, sildenafil significantly increases the rate of restored potency compared to placebo (OR = 4.66; 95% CI: 1.79–12.11). IIEF-5 in the sildenafil group is higher by ~4.7 points. The more fully the nerve bundles were preserved, the higher the probability of response to the drug.[6]

It is important to understand: sildenafil does not work in the complete absence of nerve innervation (for example, with severe neuropathy or complete damage to nerve bundles during surgery). In such cases, alternative treatment methods are considered.

Side effects

Sildenafil is well studied — adverse reactions are known, predictable, and in the vast majority of cases are mild and reversible. The discontinuation rate due to side effects in clinical trials was 2.5% — practically no different from 2.3% in the placebo group.

Common (in 2–16% of patients)

Headache, facial flushing, dyspepsia (heartburn, abdominal discomfort), nasal congestion, color vision impairment. All these reactions are dose-dependent and resolve on their own after a few hours.

Uncommon (0.1–1%)

Dizziness, visual disturbances (blurred vision), diarrhea, rash.

Rare but serious (<0.1%)

Priapism — a painful erection lasting more than 4 hours. Requires immediate medical attention. If delayed, irreversible tissue damage is possible. The risk is higher in patients with sickle cell anemia, leukemia, myeloma.
NAION (non-arteritic anterior ischemic optic neuropathy) — sudden loss of vision, usually in one eye. The connection with PDE-5 inhibitors is debatable; the risk is higher in patients with pre-existing risk factors (diabetes, hypertension, crowded optic disc).
Sudden hearing loss — isolated cases have been described, a causal relationship has not been established.
Color vision impairment ("blue haze") — specific to sildenafil. The molecule partially inhibits retinal PDE-6, which is responsible for color vision, hence the temporary bluish or greenish tint of the picture. Of the five PDE-5 inhibitors, this effect is most pronounced in sildenafil; in tadalafil and avanafil, it is practically absent.

Practical advice: if you notice a change in color perception after taking the drug, refrain from driving at twilight or at night until the action of the drug stops (usually after 4–6 hours). In daylight, color perception is usually not impaired to a clinically significant degree.

Contraindications

Absolute (cannot be taken under any circumstances)

Nitrates in any form — nitroglycerin, isosorbide dinitrate/mononitrate, isoket spray, nitrospray, drugs with "nitro-" in the composition. Co-administration causes a sharp and potentially life-threatening drop in blood pressure. This is the most critical interaction of sildenafil.
Riociguat (Adempas®) — a drug for pulmonary hypertension, also enhances the action of nitric oxide. Co-administration is contraindicated.
Severe cardiovascular diseases in which sexual activity is contraindicated: unstable angina, recent myocardial infarction (<3 months), stroke (<6 months), severe heart failure (NYHA class III–IV), uncontrolled arrhythmias, uncontrolled hypertension (>170/110 mm Hg) or hypotension (<90/50 mm Hg).
Severe hepatic insufficiency (Child-Pugh class C) — clearance of sildenafil is sharply reduced.
Loss of vision in one eye due to a history of NAION — risk of a repeat episode.
Hypersensitivity to sildenafil or any of the auxiliary components.
Age under 18 years.

Relative (require caution and consultation with a doctor)

Stable ischemic heart disease, chronic heart failure of NYHA class I–II, hypertension under medical control — use is possible, but only after assessing cardiac risk.

Anatomical deformities of the penis (Peyronie's disease, cavernous fibrosis, severe curvature) — increased risk of priapism.

Diseases predisposing to priapism: sickle cell anemia, leukemia, multiple myeloma.

Retinitis pigmentosa — PDE-6 disorders in this case are potentially dangerous.

Moderate renal insufficiency (creatinine clearance 30–80 ml/min) — requires dose adjustment (start with 25 mg).

Moderate liver function impairment (Child-Pugh A–B) — start with 25 mg.

Drug interactions

Critically dangerous — absolute contraindication

Nitrates and nitric oxide donors (nitroglycerin, isosorbide, amyl nitrite, and others). Combined use can cause critical hypotension. If you take nitrates regularly, sildenafil is completely contraindicated. If you took a nitrate urgently (nitroglycerin under the tongue for heart pain), at least 24 hours must pass before the next dose of sildenafil. And vice versa: after taking sildenafil, nitrate cannot be taken for at least 24 hours.

Riociguat — contraindicated.

Require dose adjustment

Strong CYP3A4 inhibitors (ketoconazole, itraconazole, erythromycin, clarithromycin, ritonavir, and other HIV protease inhibitors) — significantly increase the concentration of sildenafil in the blood. When co-administered with ritonavir, the AUC of sildenafil increases 11-fold. The maximum dose when co-administered with ritonavir is 25 mg once every 48 hours. With moderate CYP3A4 inhibitors — start with 25 mg.

Alpha-blockers (doxazosin, tamsulosin — used for prostate adenoma) — additive hypotensive effect. When used together, start with 25 mg, take 4 hours after the alpha-blocker. Tamsulosin (highly selective) combines better than non-selective drugs.

Practically do not affect pharmacokinetics

CYP2C9 inhibitors (warfarin, tolbutamide), CYP2D6 inhibitors (SSRIs, tricyclic antidepressants), thiazide diuretics, ACE inhibitors, calcium channel blockers — no significant clinically relevant interaction was found.

Moderate interactions

Antacids (magnesium hydroxide + aluminum hydroxide) reduce the rate of absorption of sildenafil, but not the AUC. Grapefruit juice inhibits CYP3A4 in the intestine — best to avoid.

If you are taking several medications, be sure to check possible interactions with your doctor or pharmacist. Especially if among them there are drugs for the heart, pressure, or fungal infections.

Special patient groups

Elderly men (65+)

In elderly patients, sildenafil clearance is reduced, so the concentration in the blood at the same dose is higher. The recommended starting dose is 25 mg. The official Viagra instructions state: if 25 mg is well tolerated, the dose can be increased to 50 and 100 mg if necessary.[2]

Diabetes mellitus

Sildenafil is effective for diabetic ED, but the response in this group is somewhat lower than in patients without diabetes. Neuropathy and vascular disorders reduce sensitivity to the drug. The starting dose is 50 mg, with insufficient effect — 100 mg. With poorly controlled diabetes, glycemic correction is necessary.

Kidney diseases

Mild and moderate renal insufficiency (CrCl 30–80 ml/min) — pharmacokinetics do not change significantly, the standard dose is acceptable. In severe renal insufficiency (CrCl <30 ml/min), the AUC increases approximately twofold — start with 25 mg.

Liver diseases

Mild and moderate impairments (Child-Pugh A–B) — clearance is reduced, AUC increases by 84%, Cmax by 47%. Starting dose — 25 mg. Severe hepatic insufficiency (Child-Pugh C) — sildenafil is contraindicated.

Cardiovascular diseases

Controlled hypertension and stable IHD are not absolute contraindications. The decision to start therapy is made jointly with a cardiologist, taking into account the functional class of CHF and physical activity tolerance.

What to do if...

...the drug did not work

This happens, and quite often — especially with the first dose. The most common reasons are:

Taking after a fatty meal (delays absorption by 1–2 hours).
Too short waiting time — less than 30 minutes.
Insufficient sexual excitement: sildenafil enhances the response to stimulation, but does not replace it.
High anxiety during the first use — the psychological factor really reduces effectiveness.
Washing down with tea, coffee, juice instead of water.

Manufacturer's recommendations: evaluate the effectiveness by at least 4–8 attempts in different conditions. If 50 mg does not work, try 100 mg. If 100 mg is also ineffective after several doses, consult a doctor to find out the cause of ED.

...side effects occurred

Mild side effects (headache, facial flushing, nasal congestion, mild stomach upset) — usually pass on their own within 2–4 hours. No action is needed. Next time you take it, try reducing the dose.
Color vision impairment ("blue haze") — a temporary phenomenon, passes as the concentration of the drug in the blood decreases. During this period, refrain from driving at twilight and at night.
Sudden dizziness or drop in pressure — lie down, raise legs above heart level, drink water. If the condition does not improve or you have consumed alcohol, call an ambulance.
Chest pain — call an ambulance immediately. Do not take nitroglycerin: co-administration with sildenafil causes a critical drop in pressure. Inform the medical staff that you took sildenafil and when.

...the erection does not go away (priapism)

If the erection is painful and does not subside within 2–3 hours after the end of sexual activity, this is an emergency situation. Do not wait for 4 hours.

Immediately contact the nearest emergency room or call an ambulance. Treatment of priapism started in the first 4–6 hours, as a rule, allows to fully restore function. Delay threatens irreversible damage to the cavernous bodies and permanent impotence.

This is a rare complication (<0.1%), but you need to know about these symptoms in advance.

...an excessive dose was taken (overdose)

There is no specific antidote. Symptoms of overdose are a continuation and intensification of side effects: severe headache, severe facial flushing, sharp drop in pressure, dizziness, visual disturbances.

Actions:

Stop taking, lie down, ensure rest.
In case of a significant drop in pressure or loss of consciousness, call an ambulance.
Tell the doctor what dose and when you took.
Do not take nitrates (nitroglycerin) to relieve chest pain — this is dangerous.

In most cases, an overdose resolves on its own as the drug is eliminated (half-life ~4 hours). Dialysis is ineffective due to the high degree of sildenafil binding to plasma proteins.

...missed a dose

Sildenafil is taken "on demand" — only before planned sexual activity, and not on a schedule. Therefore, the concept of a "missed dose" is not applicable to it. Just take the drug next time you need it, keeping an interval of at least 24 hours between doses.

Storage conditions

Store at a temperature not exceeding 30°C, in a dry place protected from direct sunlight. Keep out of reach of children. Expiry date — indicated on the package, usually 3 years. Do not use after the expiry date.

Sildenafil-based drugs in our catalog

All listed drugs contain sildenafil citrate as the active substance. This instruction applies to all of them. Differences between brands are in the manufacturer, auxiliary components, and packaging design; the mechanism of action, indications, contraindications, and interactions are identical.

Sildenafil 25 mg — Malegra 25, Cenforce 25, and others
Sildenafil 50 mg — Kamagra 50, Malegra 50, Cenforce 50, Fildena 50, and others
Sildenafil 100 mg — Kamagra 100, Malegra 100, Cenforce 100, Fildena 100, Suhagra 100, Silagra 100, and others
Sildenafil 150 mg — Cenforce 150, Fildena 150, Malegra 150, and others
Sildenafil 200 mg — Cenforce 200, Fildena 200, Malegra 200, and others
Sildenafil Soft / Oral Jelly — Kamagra Oral Jelly, Kamagra Chewable, Kamagra Effervescent, and other fast forms

If you have questions about a specific brand, check the page of that drug — it describes the features of the specific dosage and release form.

The information on this page is for guidance only and does not replace consultation with a doctor. Before the first use of any sildenafil-based drug, consult a urologist or general practitioner — especially in the presence of cardiovascular diseases, taking other medications, or chronic illnesses.

Frequently Asked Questions

How does generic Sildenafil differ from Viagra?

The active substance is the same — sildenafil citrate in the same dosage. The mechanism of action, effectiveness, and safety profile are identical. The difference is in the brand name, manufacturer, and price. Generics are released after the patent protection of the original expires and are produced according to GMP standards. The price of generics is 3–10 times lower because the manufacturer does not incur costs for clinical trials of the molecule.

How long does it take to start working?

The peak concentration in the blood is reached 30–120 minutes after taking on an empty stomach (median is about 60 minutes). The first effect in some men occurs as early as 15–20 minutes, in others — in an hour or more. Fatty food delays absorption by about 1 hour. For a stable result, plan to take it 45–60 minutes before intimacy.

How long does the action last?

The half-life of sildenafil is about 3–4 hours. A clinically significant effect lasts for about 4–6 hours. This does not mean that the erection lasts for 6 hours — it occurs only during sexual arousal. After the drug stops working, the erection does not differ from the usual one.

Can it be taken every day?

Can it be taken with hypertension?

Controlled hypertension is not an absolute contraindication. Key conditions: blood pressure is medically controlled (less than 170/110 mm Hg) and you do not take nitrates. Be sure to inform your doctor about all hypotensive drugs — especially if among them there are alpha-blockers (doxazosin and analogs), as they enhance the reduction of blood pressure.

Does it cause addiction or dependence?

Physical dependence does not form. Sildenafil is not a drug or a hormone; after stopping use, the function of the penis returns to its original level. Psychological "dependence" is sometimes mentioned in the context of a man being "afraid without a pill" — but this is not a pharmacological phenomenon, but a behavioral feature.

Sources

[1] FDA. Drug Approval Package: Viagra (sildenafil citrate) NDA 020895. Approved: March 27, 1998. FDA.gov
[2] Goldenberg M.M. Safety and efficacy of sildenafil citrate in the treatment of male erectile dysfunction. Clinical Therapeutics, 1998; 20(6): 1033–1048. PubMed: 9916601
[3] Muirhead G.J. et al. Pharmacokinetics of sildenafil after single oral doses in healthy male subjects: absolute bioavailability, food effects and dose proportionality. British Journal of Clinical Pharmacology, 2002. PMC: 1874258
[4] Boulton A.J. et al. Sildenafil citrate for the treatment of erectile dysfunction in men with Type II diabetes mellitus. Diabetologia, 2001; 44(10): 1296–1301. PubMed: 11692178
[5] Shah P.C., Trivedi N.A. A meta-analysis on efficacy and tolerability of sildenafil for erectile dysfunction in patients with diabetes mellitus. Indian Journal of Sexually Transmitted Diseases and AIDS, 2018; 39(1): 1–6. PubMed: 30187018
[6] Lu X. et al. Efficacy of sildenafil citrate in men with erectile dysfunction following bilateral nerve-sparing radical prostatectomy: systematic review and meta-analysis. Zhonghua Yi Xue Za Zhi, 2015; 95(36): 2964–2968. PubMed: 26814076
[7] FDA Label — Viagra® (sildenafil citrate) Tablets. Prescribing Information. FDA.gov (PDF)

The sources describe the sildenafil molecule and apply to all drugs based on it — both the original Viagra® and generics.