The difference between ED medication working well and not working at all often comes down to timing. And the gap between treatments is bigger than most men realise.
Clinical trials using stopwatches at home have produced precise data on how quickly each medicine starts working. This article breaks down what those studies actually found.
You still need to feel aroused for any ED tablet to work. They help your body respond, they don't create an erection on their own.
Why timing matters
All four ED treatments available at Pharmica, sildenafil, tadalafil, vardenafil and avanafil, block an enzyme called PDE5. That increases blood flow to the penis when you're sexually stimulated. None of them causes an erection without arousal.
Plenty of men give up on their first ED treatment, not because it didn't work, but because they took it at the wrong time. Getting the timing wrong, and not enough sexual stimulation, are among the most common fixable reasons these medicines seem not to work.
Understanding what the trials found for each treatment gives you a clearer picture of how each one behaves, and a better chance of getting it right first time.
What "onset" means in the clinical trials
Before going through each treatment, it helps to know how "onset" is measured in these trials.
The gold standard is time to successful intercourse. Men used a stopwatch from the moment they took the dose until they had an erection firm enough for penetration that led to completed sex. It's a real-world measure of what matters, not a lab measure of how much medicine is in the blood.
A separate type of study used devices called RigiScan monitors to pick up very early changes in erection firmness in a clinic. These sometimes showed effects even earlier than the stopwatch studies.
Both types of study are referenced below. But the at-home stopwatch trials are the most useful in practice.
Sildenafil: what the stopwatch studies found
Sildenafil's prescribing information says to take it 30 to 60 minutes before sex, with effects possible from 30 minutes up to 4 hours after the dose. A landmark trial designed specifically to measure the fastest time it starts working added useful detail.
The trial involved 228 men who were known to respond to sildenafil (115 on sildenafil 100mg, 113 on placebo). They took their dose at least 2 hours after eating, and used a stopwatch from dose to an erection good enough for successful sex.
Sildenafil was already working better than placebo at 14 minutes. By 20 minutes, 51% of men on sildenafil had an erection good enough for sex, compared with 30% on placebo. The middle (median) time to an erection that led to successful sex was 36 minutes.1
First time on sildenafil? Give it a few tries before deciding it doesn't work. It often takes more than one go to get it right.
That's noticeably faster than the packaging suggests. The 60-minute instruction reflects when blood levels usually peak (anywhere from 30 to 120 minutes, typically 60). But the trial showed the medicine can start working well before that peak.
In practice, sildenafil can work within 30 minutes for many men, but it's most reliable at around 45 to 60 minutes when taken on an empty stomach.
Tadalafil: earlier onset than most men expect
Tadalafil stays in your body far longer than any other licensed PDE5 inhibitor. Its half-life is around 17.5 hours, which is behind its 36-hour window and the daily 5mg option.
Its blood levels peak at around 2 hours, much later than sildenafil, which leads many men to assume it's slow to start working. A dedicated at-home trial tested that assumption.
In the trial, men with ED tried to have sex within 30 minutes of taking tadalafil 10mg, 20mg or placebo, on four separate occasions, timing it with a stopwatch.
The key finding: tadalafil 20mg was working measurably better than placebo from 16 minutes after the dose. 52% of men on tadalafil 20mg had at least one successful attempt within 30 minutes, compared with 35% on placebo.2
Tadalafil's long window takes the pressure off. If the first hour doesn't go to plan, it's still working for many hours afterwards.
So tadalafil starts working noticeably earlier than its peak blood level would suggest. Even before levels peak, there's enough of the medicine to have an effect for many men.
In practice, you can take on-demand tadalafil (10mg or 20mg) 30 minutes before sex. And if the first hour doesn't work out, it stays active for far longer than sildenafil.
Vardenafil (Levitra): the fastest first-generation option
Vardenafil, also sold as Levitra, reaches peak blood levels at a similar time to sildenafil, around 45 to 60 minutes. But the at-home stopwatch data suggests it may start working slightly earlier for some men.
A large at-home trial involved 732 men: 237 on vardenafil 10mg, 248 on vardenafil 20mg and 247 on placebo. They recorded the time from dose to an erection firm enough for penetration with a stopwatch, over their first four doses.
Vardenafil worked better than placebo from as early as 10 to 11 minutes after the dose in men who responded.3 Looking back at the data, 75 to 77% of attempts made within 15 minutes of dosing were successful in men taking vardenafil, compared with 45 to 47% on placebo.
Across the three first-generation medicines, the earliest response times look like this: around 35% of men on sildenafil responded from 14 minutes, 32% on tadalafil from 16 minutes, and 23% on vardenafil from 11 minutes.1,2,3
These come from separate trials, so they aren't a direct comparison. The differences at the earliest time points are small. For most men, the more useful difference between vardenafil and sildenafil isn't how fast they work, but how food affects them.
Avanafil (Spedra): the timing case for a second-generation drug
Spedra (avanafil) was designed specifically to work faster than the first-generation PDE5 inhibitors. Its blood levels peak at around 30 to 45 minutes.
Do not take an ED tablet if you use nitrates for chest pain, or poppers. The combination can cause a dangerous drop in blood pressure.
A randomised trial of 440 men with ED looked at successful sex within around 15 minutes of taking avanafil 100mg, 200mg or placebo, over 8 weeks, using a stopwatch.
Both doses of avanafil led to significantly more successful attempts within 15 minutes than placebo. The difference was significant from 10 minutes after the dose with 200mg, and from 12 minutes with 100mg.4
A separate head-to-head trial comparing avanafil directly with sildenafil found that more avanafil doses led to an erection within 15 minutes. That confirmed faster onset as a genuine feature of the medicine, not just a marketing claim.5
So avanafil is the option to consider if the 30 to 60-minute planning window of first-generation medicines really doesn't work for you. You can take it around 15 to 30 minutes before sex. Like sildenafil, it may take longer to work if you take it with food.6
How food changes the timing equation
Food is where the timing differences between treatments matter most in practice, and where the clinical data is most specific.
Sildenafil is the most affected by food of the four. A high-fat meal delays its peak blood level by around an hour, and lowers the peak level by 29%.7
A dedicated trial on food and dose timing confirmed that taking sildenafil with a high-fat meal made it noticeably less reliable early on, compared with taking it on an empty stomach.8 Food is the single most controllable thing affecting how quickly sildenafil works. On an empty stomach, it's predictable. After a big meal, it isn't.
Vardenafil is affected by food in a similar way. High-fat meals can noticeably delay how quickly standard vardenafil tablets work, mainly because your stomach empties more slowly.9 The same advice applies: take it on an empty stomach or after a light meal.
Tadalafil isn't meaningfully affected by food. That's a well-established difference, and a practical advantage if timing around meals is difficult for you.
Planning a dinner date? Tadalafil isn't affected by food, so it's the easiest to time around a meal.
Avanafil can be taken with or without food, but a meal may delay when it starts working.6
What this means for choosing a treatment
The trial data on timing points to a few practical conclusions.
Chest pain during sex, or an erection lasting more than four hours? Get urgent medical help.
If spontaneity and minimal planning matter most, avanafil (Spedra) has the most clinical evidence behind a 15-minute onset. It outperformed a first-generation treatment on speed in a direct comparison.
If you can plan ahead and how long it lasts matters more, tadalafil gives you a 36-hour window, with onset from around 30 minutes for most men. The daily 5mg version takes timing decisions out of the picture entirely.
If you want the most studied option, sildenafil has the largest evidence base and genuinely early onset. But managing food around your dose makes a real, measurable difference to how quickly it works.
Vardenafil (Levitra) sits in similar territory to sildenafil on timing.
Not sure which suits you? The ED Trial Pack lets you compare sildenafil and tadalafil before committing to one. The full range of ED treatments available at Pharmica includes all four active ingredients discussed in this article.
Frequently asked questions
How long does Viagra take to work?
A clinical trial using at-home stopwatches found that sildenafil produced a statistically superior response to placebo from as early as 14 minutes after dosing. By 20 minutes, 51% of men had achieved an adequate erection, and the median time to successful intercourse was 36 minutes. In practice, most men find peak reliability sits between 45 and 60 minutes when taken fasted. The 60-minute instruction on the packaging reflects the time to peak plasma concentration, not the time to effect, which can arrive considerably earlier.
How long does Viagra last?
Sildenafil typically remains effective for 4 to 6 hours after taking it. This refers to the window during which an erection can be achieved in response to sexual stimulation, not the duration of any single erection. Its half-life is approximately 3 to 5 hours, meaning concentrations fall progressively after that point. Taking a higher dose does not extend this window: 25mg and 100mg tablets have similar durations of action.
When should you take Viagra before sex?
Clinical evidence suggests sildenafil can work in under 30 minutes for many men, but peak reliability is closer to 45 to 60 minutes when taken on an empty stomach or after a light meal. If you have eaten a large, high-fat meal, absorption can be delayed by up to an hour and peak concentration reduced by around 29%, so waiting at least 2 hours after eating before dosing is advisable. The exact timing window that works for you may take a few attempts to establish.
Can you drink alcohol with Viagra?
One or two drinks are unlikely to prevent sildenafil from working. However, both alcohol and sildenafil lower blood pressure, and combining them in larger amounts can cause an additive drop that leads to dizziness, flushing, or lightheadedness. Heavy drinking can also directly impair the ability to achieve an erection independently of medication. The clinical advice is to keep alcohol to a minimum on any occasion when taking ED medication.
How long does sildenafil last compared to tadalafil?
Sildenafil remains effective for 4 to 6 hours, while on-demand tadalafil (10mg or 20mg) lasts up to 36 hours after a single dose. This difference in duration is the main practical distinction between the two. Both can produce a response from around 30 minutes after dosing. Daily tadalafil (5mg), taken every day rather than as needed, maintains a consistent background level of the drug so that timing relative to sexual activity is not a factor.
References
- Eardley I, et al. Minimal time to successful intercourse after sildenafil citrate: results of a randomized, double-blind, placebo-controlled trial. Urology. 2003;62(3):400-403. goldjournal.net
- Rosen RC, et al. Determining the earliest time within 30 minutes to erectogenic effect after tadalafil 10 and 20 mg: a multicenter, randomized, double-blind, placebo-controlled, at-home study. J Sex Med. 2004;1(2):193-200. pubmed.ncbi.nlm.nih.gov
- Montorsi F, et al. Earliest time to onset of action leading to successful intercourse with vardenafil determined in an at-home setting: a randomized, double-blind, placebo-controlled trial. J Sex Med. 2004;1(2):168-178. pubmed.ncbi.nlm.nih.gov
- Hellstrom WJG, et al. Efficacy of avanafil 15 minutes after dosing in men with erectile dysfunction: a randomized, double-blind, placebo-controlled study. J Sex Med. 2015;12(5):1202-1208. pubmed.ncbi.nlm.nih.gov
- Kaul S, et al. Efficacy and safety of avanafil as compared with sildenafil in the treatment of erectile dysfunction: a randomized, double blind, multicenter clinical trial. Andrologia. 2022;54(7):e14452. pmc.ncbi.nlm.nih.gov
- Menarini International. Spedra (avanafil) Summary of Product Characteristics. Electronic Medicines Compendium (eMC). medicines.org.uk/emc
- Muirhead GJ, et al. Pharmacokinetics of sildenafil after single oral doses in healthy male subjects: absolute bioavailability, food effects and dose proportionality. Br J Clin Pharmacol. 2002;53(Suppl 1):5S-12S. pmc.ncbi.nlm.nih.gov
- Donatucci CF, et al. Do food and dose timing affect the efficacy of sildenafil? A randomized placebo-controlled study. J Sex Med. 2011;8(10):2927-2935. sciencedirect.com
- Rajagopalan P, et al. Effect of high-fat breakfast and moderate-fat evening meal on the pharmacokinetics of vardenafil. J Clin Pharmacol. 2003;43(3):260-267.
This article is intended for informational purposes only and does not replace professional medical advice. Always read the patient information leaflet supplied with your medication and speak to a healthcare professional if you have specific concerns.