Sildenafil Doses Explained: 25 mg, 50 mg and 100 mg

Sildenafil for ED is sold in 25 mg, 50 mg and 100 mg tablets (the 20 mg tablet sold under a different name is a pulmonary-hypertension product and is not the ED label). The MedlinePlus monograph and the prescribing information behind it set the usual starting dose at 50 mg, taken as needed roughly an hour before sexual activity, with a window of 30 minutes to 4 hours.

From there the dose moves in one of two directions, and only on a clinician's say-so: up to 100 mg if 50 mg is well tolerated but not effective enough, or down to 25 mg if 50 mg works but the side effects are bothersome. It never goes above 100 mg, and it is never taken more than once in 24 hours.

The label names specific groups for whom 25 mg is the considered starting dose, because the drug clears more slowly or reaches higher blood levels:

• Men aged 65 and over.
• Men with severe kidney impairment or liver impairment.
• Men taking drugs that strongly inhibit the enzyme that breaks sildenafil down, including certain antifungals, HIV protease inhibitors and some antibiotics.
• Men on alpha-blockers, who should be stable on the alpha-blocker before adding sildenafil and then start at 25 mg to limit the drop in blood pressure.

Telling the intake form the truth about your age, medications and health is what lets an online clinician get this right. The clinics in our ED treatment comparison all run that review before a prescription is written.

It is tempting to assume 100 mg means a better erection. It does not. Sildenafil works by improving blood flow in response to stimulation; once there is enough drug on board to do that, extra milligrams add side effects, not firmness. The most common side effects on the label - headache, flushing, indigestion, nasal congestion, a bluish or blurred tinge to vision, back pain, dizziness - are more frequent at higher doses. The right dose is the lowest one that works reliably, which is exactly why the label starts in the middle and adjusts.

Rare serious effects do not scale neatly with dose, but they are the ones to know: an erection lasting more than four hours, sudden vision loss, and sudden hearing loss all mean stop and get help now. Our ED medication side effects guide has the full list.

Before concluding a dose is too low, clinicians check the things that make a correct dose look like a failure:

• It was taken with or right after a heavy, high-fat meal, which the label notes delays absorption by about an hour on average.
• It was taken too close to sex, before it had been absorbed, or too long before.
• There was little sexual stimulation; the drug does not work without it.
• Anxiety on the first few attempts. Many clinicians suggest several tries at a dose before judging it.
• Heavy alcohol, which makes erections harder on its own.

If none of those apply, a dose increase, a switch to tadalafil, or in some men a compounded multi-ingredient option are the normal next steps, all through the prescriber. Our timing guide covers the practical side in detail.

Some men are prescribed a higher-strength tablet to split, a practice that is between you and your prescriber and your pharmacist: it depends on the tablet, the dose and your dexterity, and it is never something to decide alone. Likewise, the online clinics that sell sildenafil by the dose price the three strengths differently, so the dose a clinician chooses affects what you pay. The ED cost index tracks each clinic's published price per strength, and our ED treatment cost guide explains what drives the differences.

This article is general information, not medical advice. Do not start, stop or change any medication without a licensed clinician who knows your full health history.