The normal starting dose of sildenafil for erectile dysfunction is 50 mg, taken about one hour before sexual activity. From there, the dose can be adjusted down to 25 mg or up to a maximum of 100 mg, depending on how well it works and how your body handles it. The limit is one dose per day.
Standard Doses for Erectile Dysfunction
Sildenafil comes in three strengths for ED: 25 mg, 50 mg, and 100 mg. Most people start at 50 mg. You take it roughly an hour beforehand, though it can be effective anywhere from 30 minutes to 4 hours before sexual activity. Based on your response, the dose gets adjusted up or down. The 100 mg tablet is the ceiling, and you should never take more than one dose in a 24-hour period regardless of the strength.
Adults 65 and older typically start at the lower 25 mg dose rather than 50 mg. The same lower starting point applies if you take alpha-blockers (commonly prescribed for an enlarged prostate or high blood pressure). In that case, you should already be stable on the alpha-blocker before adding sildenafil, and 25 mg is the recommended starting point to reduce the risk of a blood pressure drop.
Doses for Pulmonary Arterial Hypertension
Sildenafil is also prescribed under a different brand name for pulmonary arterial hypertension (PAH), a condition involving high blood pressure in the lungs. The dosing looks completely different: 5 mg or 20 mg taken three times a day, spaced 4 to 6 hours apart. Unlike the ED version, this is a daily medication on a fixed schedule. If you miss a dose, take it as soon as you remember, but skip it if you’re close to the next scheduled dose. Never double up.
Why Your Dose Might Be Lower
Several factors can change what counts as a “normal” dose for you personally. Age is one: older adults tend to clear the drug more slowly, so a lower dose produces the same blood levels that a younger person would get from 50 mg. Liver problems have a similar effect, since the liver is responsible for breaking sildenafil down. Kidney impairment can also slow clearance.
Certain medications change the equation as well. Drugs that inhibit the same liver pathway sildenafil uses for metabolism can effectively amplify its effects, meaning a standard 50 mg dose hits harder than expected. If you take any of these, a prescriber will often start you at 25 mg.
Medications That Don’t Mix With Sildenafil
The most important safety issue with sildenafil is the interaction with nitrates, a class of drugs used for chest pain and heart disease. Combining sildenafil with any form of nitrate can cause a dangerous, potentially life-threatening drop in blood pressure. This isn’t a matter of adjusting the dose. The combination is flatly contraindicated. If you’ve taken sildenafil within the past 24 hours and experience a cardiac event, nitrates should be avoided entirely during that window.
On its own, sildenafil causes mild, temporary decreases in blood pressure through the relaxation of blood vessels. For most people this shows up as a headache or facial flushing, nothing more. But in people already on blood pressure medications, or those with underlying cardiovascular conditions, the blood pressure drop can be more significant. That’s why the starting dose matters: beginning at 25 mg gives room to see how your body responds before moving higher.
Timing and How to Take It
For ED, the one-hour-before guideline is a general target, not a hard rule. Sildenafil can work as quickly as 30 minutes in some people. A heavy or high-fat meal can slow absorption and delay the onset, so taking it on a lighter stomach tends to produce more predictable timing. Since it’s taken as needed rather than on a schedule, there’s no concept of a “missed dose” for ED use.
The drug’s effects typically last 4 to 6 hours, though this varies. That doesn’t mean you’ll have a continuous effect for that entire window. It means sildenafil remains active in your system long enough to be useful if the moment arises within that timeframe. Regardless of how long the effects seem to last, the once-per-day limit applies.