Sildenafil Doses: How Much, and When the Label Says Less

The three labeled sildenafil doses, side effects by dose, and the situations where the label says to start low.

The Viagra label gives three sildenafil doses for ED: 25, 50 and 100 mg. Most men start at 50 mg about an hour before sexual activity, and the label allows a move up to 100 mg or down to 25 mg based on effectiveness and tolerability, no more than once a day.¹ Which dose a man actually needs depends on more than preference. The label names specific situations, from age over 65 to ritonavir, where it advises starting at 25 mg, and one, nitrates, where no dose is safe.¹

What are the standard sildenafil doses for ED?

Generic sildenafil tablets for ED carry the same instructions: 25, 50 and 100 mg tablets, 50 mg as the usual dose, a window of 30 minutes to 4 hours before sexual activity, and a maximum of once per day.² The dose is a starting point to adjust, not a fixed prescription. Our sildenafil 50 mg guide covers the middle strength in detail, and sildenafil 20 mg explains why that tablet belongs to a different label.

Those percentages come from fixed-dose Phase II/III studies with 312 men on 25 mg, 511 on 50 mg, 506 on 100 mg and 607 on placebo.¹ Flushing, indigestion and abnormal vision, mostly a color tinge to vision, also rose with dose; abnormal vision was 11% at 100 mg against 2% at 50 mg.¹ The label states that scores improved more at 50 and 100 mg than at 25 mg.¹

Who should start on 25 mg?

The label asks prescribers to consider 25 mg as the starting dose in four groups, because their blood levels of sildenafil run higher.¹

• Men over 65. In healthy volunteers aged 65 or older, sildenafil clearance was reduced and exposure (AUC) was about 84% higher than in young volunteers. The label reports no overall difference in safety or efficacy by age but advises a 25 mg start because higher levels may raise side effects.¹
• Liver impairment. In volunteers with mild to moderate impairment (Child-Pugh A and B), peak levels were 47% higher and exposure 85% higher. The label suggests 25 mg for any degree of impairment and says severe impairment has not been studied.¹
• Severe kidney impairment. With creatinine clearance below 30 mL/minute, exposure roughly doubled. No adjustment is needed for mild or moderate kidney impairment.¹
• Some interacting medicines. See the next two sections.¹

Age alone does not mean sildenafil is less useful. A pooled analysis of 48 placebo-controlled trials in 11,364 men found improvement over placebo in every age group, though the share reporting better erections fell with age: 80% under 65, 69% at 65 to 74 and 59% at 75 or older. The analysis was funded by Pfizer, which makes Viagra, and the trials began at 50 mg with adjustment to 100 or 25 mg.³

What if you take an alpha-blocker or blood pressure medicine?

The Viagra label says that when sildenafil is taken with an alpha-blocker, the patient should be stable on the alpha-blocker first, and sildenafil should be started at 25 mg.¹ Alpha-blockers are prescribed for high blood pressure and for urinary symptoms from an enlarged prostate. The reason is additive blood pressure lowering. The label lists hypotension with alpha-blockers or antihypertensives among its warnings.¹ Our guide to ED and blood pressure medicines goes through the trial evidence.

Which drug interactions change the dose?

Two groups of drugs slow the breakdown of sildenafil. For ritonavir, the label recommends 25 mg before sexual activity and a maximum of 25 mg in 48 hours, because ritonavir raised sildenafil levels 11-fold. For strong CYP3A4 inhibitors such as ketoconazole, itraconazole or saquinavir, and for erythromycin, it says to consider a 25 mg start; saquinavir and erythromycin raised levels about 3-fold.¹

The bigger line is not a dose at all. Sildenafil is contraindicated with any form of organic nitrate, whether taken regularly or occasionally, and with guanylate cyclase stimulators such as riociguat. The label says it is unknown when nitrates can safely be given after sildenafil.¹ Do not use a lower dose to get around these. Our ED medication interactions guide covers the full list.

Can you take more than 100 mg or more than once a day?

No. The maximum recommended dose is 100 mg and the maximum frequency is once per day.¹ Taking two 50 mg tablets is a 100 mg dose, so it uses the whole day's allowance. Likewise the 20 mg PAH tablets are not a way to build an ED dose; that product has its own labeled schedule.⁴ An erection lasting more than 4 hours needs immediate medical help, per the label.¹

When is the dose raised or lowered?

By the prescriber, from response. If 50 mg is not enough and is well tolerated, 100 mg is the next step; if side effects are a problem, 25 mg is the label's lower option.¹ Some practical details come from the label: a high-fat meal delays absorption by about an hour and lowers the peak level by 29%, which can feel like a weaker dose when it is really a timing effect (see sildenafil with or without food).¹ MedlinePlus lists sildenafil (Viagra) as a treatment for erectile dysfunction.⁵ The label notes a response needs sexual stimulation.¹ The American Urological Association guideline treats PDE5 inhibitors as a standard option and expects dose and drug to be individualized.⁶

Questions to ask a prescriber about dose

• Do my age, liver, kidneys or other medicines change the starting dose?
• Do I take a nitrate, an alpha-blocker or HIV medicine?
• How long should I try a dose before changing it?
• Which symptoms mean I should stop and call, and which mean emergency care?

Questions readers ask

What is the usual sildenafil dose for ED?

The Viagra label recommends 50 mg about an hour before sexual activity for most men. It may be raised to 100 mg or lowered to 25 mg, and should not be taken more than once a day.

Who should start on 25 mg of sildenafil?

The label says to consider 25 mg for men over 65, men with liver impairment, men with severe kidney impairment, and men taking strong CYP3A4 inhibitors or erythromycin. With an alpha-blocker, it says to start at 25 mg.

Is 100 mg of sildenafil the maximum?

Yes. The label's maximum recommended dose is 100 mg and the maximum frequency is once per day.

Does a higher sildenafil dose cause more side effects?

In the label's fixed-dose trials, headache, flushing, indigestion and abnormal vision were generally more common at 100 mg than at 25 mg.

Can I take sildenafil with nitrates at a low dose?

No. The label contraindicates sildenafil with any form of organic nitrate, and a lower dose does not change that.

Further reading

Part of our guide: How ED Medications Work: Timing, Food, Interactions and Combinations

• Sildenafil Headache: How Common Is It?
• Tadalafil With Alcohol: How Much Is Too Much?
• What Is Tadalafil Used For? The Three Approved Uses
• Tadalafil Brand Names: Which Brand Is Used for What