ED medication onset and duration planner

Onset, duration and why the four are not interchangeable

All four oral ED medications are PDE5 inhibitors and all four work the same way: they stop an enzyme from breaking down cGMP, so the smooth muscle in the corpus cavernosum stays relaxed for longer once sexual stimulation has started the process. None of them does anything without arousal. What separates them is not potency, it is pharmacokinetics — how quickly the tablet reaches peak concentration and how long it takes the body to clear it.

That difference is large. Avanafil is licensed to be taken as early as 15 minutes before sex; tadalafil reaches its median peak at 2 hours. Sildenafil's own label documents an effect lasting 4 hours, and weaker at 4 hours than at 2. Tadalafil's documents improved erectile function against placebo up to 36 hours after a single dose. That is not a marginal advantage, it is a different category of drug, and it is why the same man may be prescribed one for a planned evening and the other for a weekend away.

The figures below are lifted from the Structured Product Labels on DailyMed, quoted with their section numbers. Where a label does not state something, the table says so rather than filling the gap: only the sildenafil and tadalafil labels give a duration of effect, so the vardenafil and avanafil bars show terminal half-life instead and are drawn differently on the timeline.

None of this is a recommendation to take anything. These are prescription-only medicines with an absolute contraindication — organic nitrates in any form — and the choice between them belongs to the clinician who wrote the prescription. This page is for working out the timing of a medication you have already been prescribed.

ED medication comparison chart — onset, duration and food

Every figure quoted from the FDA label for that agent. Read across for the one you have been prescribed.

Sildenafil and tadalafil labels state a duration of effect; vardenafil and avanafil labels do not, so those two rows show terminal half-life and are marked as such. Maximum dosing frequency is once per day for all four.

When to take it — dose time by planned activity

The clock time to swallow the tablet, and in smaller type the full window it can be taken in.

Windows that open before midnight fall on the previous day — for tadalafil, 36 hours back, which is most of a day and a half.

How long does it last? Coverage by hours after the dose

Where each agent stands at a given number of hours after swallowing the tablet, on its own label’s figures.

“In range” means inside the span the label supports, not that an erection is present — all four require sexual stimulation to do anything at all.

Frequently asked questions

Which ED medication works the fastest?

Avanafil (Stendra). Its label instructs that the 100 mg and 200 mg doses may be taken "as early as approximately 15 minutes before sexual activity", and gives a median time to peak concentration of 30 to 45 minutes. Sildenafil and vardenafil both peak at a median of 60 minutes, and their labels put the practical lead time at 30 to 60 minutes. Tadalafil is the slowest of the four, with a median time to peak of 2 hours.

How long does 20mg tadalafil last?

The CIALIS label states that tadalafil taken as needed "was shown to improve erectile function compared to placebo up to 36 hours following dosing", and the mean terminal half-life is 17.5 hours. That 36-hour figure is an efficacy window, not a 36-hour erection — it is how long a single dose still outperformed placebo in trials. For comparison, sildenafil's label documents an effect up to 4 hours, and weaker at 4 hours than at 2.

Does food affect ED medication?

It depends which one. Sildenafil is the most affected: with a high-fat meal its label records "a mean delay in Tmax of 60 minutes and a mean reduction in Cmax of 29%", so a cheeseburger before a 50 mg tablet can push the peak back a full hour. Vardenafil's label reports a 18% to 50% reduction in peak concentration with high-fat meals. Avanafil's peak is delayed about 1.1 to 1.25 hours and cut 39%, which its label calls clinically minimal. Tadalafil is the exception: "the rate and extent of absorption of tadalafil are not influenced by food".

What is the difference between daily tadalafil and on-demand tadalafil?

On-demand tadalafil is 10 mg taken before anticipated sexual activity, adjustable to 5 mg or 20 mg, no more than once a day. Daily tadalafil is a lower continuous dose — the label's starting dose for once-daily use is 2.5 mg, increased to 5 mg based on response, "taken at approximately the same time every day, without regard to timing of sexual activity". Daily dosing removes planning entirely at the cost of taking a tablet every day; the 5 mg daily dose is also the one licensed for benign prostatic hyperplasia.

Can you take ED medication with nitrates?

No. This is an absolute contraindication on all four labels, not a caution. Organic nitrates in any form — nitroglycerin, isosorbide mononitrate or dinitrate, and amyl or butyl nitrite "poppers" — taken with a PDE5 inhibitor can drop blood pressure to a dangerous level. Tadalafil’s label goes further and states that where a nitrate is medically necessary in a life-threatening situation, "at least 48 hours should have elapsed after the last dose of CIALIS". Guanylate cyclase stimulators such as riociguat are contraindicated on all four labels as well.

How long before sex should I take Viagra?

The label is explicit: "the recommended dose is 50 mg taken, as needed, approximately 1 hour before sexual activity. However, VIAGRA may be taken anywhere from 30 minutes to 4 hours before sexual activity." So one hour is the target and 30 minutes to 4 hours is the usable span. If you have eaten a fatty meal, add roughly an hour to the lead time — the label documents a 60-minute delay to peak concentration under those conditions.

Is vardenafil the same as sildenafil?

Pharmacokinetically they are close but not identical. Both reach peak plasma concentration between 30 minutes and 2 hours with a median of 60 minutes, and the vardenafil label instructs taking it approximately 60 minutes before sexual activity. Vardenafil has a slightly longer terminal half-life at approximately 4 to 5 hours against sildenafil’s 4 hours, and comes in 2.5, 5, 10 and 20 mg tablets against sildenafil’s 25, 50 and 100 mg. Unlike sildenafil, the vardenafil label states no duration of effect at all.

Why does the chart show half-life for vardenafil and avanafil instead of a duration?

Because their FDA labels do not state one. The sildenafil label documents an effect for up to 4 hours and the tadalafil label documents improved erectile function up to 36 hours, but neither the vardenafil nor the avanafil label makes a duration-of-effect claim. Rather than borrow a number from a secondary source and print it as though it were equivalent, those two bars show the terminal half-life instead — approximately 4 to 5 hours and approximately 5 hours respectively — and are drawn differently on the timeline.

Sources

1. [1]STENDRA (avanafil) tablet — Metuchen Pharmaceuticals, LLC. FDA prescribing information via DailyMed (setid fa7d93e3-b69b-4e02-8146-89760cd8e9d6)
2. [2]VIAGRA (sildenafil citrate) tablet, film coated — Pfizer Laboratories Div Pfizer Inc. FDA prescribing information via DailyMed (setid 0b0be196-0c62-461c-94f4-9a35339b4501)
3. [3]VARDENAFIL tablet, film coated — Zydus Pharmaceuticals USA Inc.. FDA prescribing information via DailyMed (setid 5876e062-e604-42a7-99c3-5da30b8dac06)
4. [4]CIALIS (tadalafil) tablet, film coated — Eli Lilly and Company. FDA prescribing information via DailyMed (setid bcd8f8ab-81a2-4891-83db-24a0b0e25895)